FOC

Chapter 1

Introduction to Computer System

Introduction

Computer has been the premier invention of this century. It plays an important role in almost every part of our lives. It has become so important that without it we would not be able to live the way we do. Look around you and you would find computers scattered all over the places, starting with the machine of computer to washing machine, refrigerator, car, mobile and to life saving devices with the doctors. Everywhere a small computer is working for your convenience and they seem to perform almost any task in the world.

Computers have had a tremendous impact on the way information is processed within an organization. Although information has been processed manually throughout the history yet in modern management where decision-making is very fast and in the era of corporate governance, it is not possible without the help of information system managed by computers.

Computer

The term ‘computer’ is derived from the word’ Compute’ which means to calculate. A computer is an electronic device that can accept data, process it according to a set of predefined instructions called program and then gives the results. In simple words, a computer is an electronic device that performs mathematical and non-mathematical operations with the help of instructions to process the information in order o achieve desired results. It has ability to accept data, input, and store and execute instructions, perform mathematical and logical operation on data and output results.

1.2 Components of Computer

A computer organization is often compared with a human brain. Just think of a human brain, how it works? It can store data with its five senses (like input devices in a computer), process the gathered information and reach to some conclusion drawn from the raw data (like the processing of a computer system). Then, it can deliver an output or result with speech or with expression (like an output device).

The major components of computer are given below:

1.      Hardware: The physical devices that make up the computer are called hardware. Hardware is any part of computer you can touch. E.g. monitor, keyboard, mouse, wires etc.

2.      Software: Software is a set of instructions that make the computer to perform tasks. [i.e. it tell the computer what to do]

3.      People: People are users of the computer system and are responsible for designing, building programs and repairing computer system.

4.      Data: Data is the raw facts and figures often used to produce the information as per the demand of the user. Data can be letters, numbers, sounds, images or videos.

5.      Procedure: It is simply the way of doing thing. Computer always performs the task based on specific procedure based on the nature of the task to be carried on.

1.3 Characteristics of Computer

The ever-increasing use of computers is due to their special characteristics. A computer is not just a calculating machine. It is also capable of doing complex activities and operations. The main characteristics of a computer are given below:

Word Length: The number of bits that a computer can process at a time in parallel is called its word length. The commonly used word lengths are 16, 32, 64 or 128 bits. It is a measure of the computing power of a computer. Computer with longer word length are more powerful. 32 bit computer means that its word length is 32 bits.

Speed: A computer is a very fast and accurate device. Since electronic pulses travel at incredible speed and are electronic devices, their internal speed is virtually instantaneous. A microcomputer can process millions of instruction per second over and over again without any mistake. A modern computer can execute millions of instruction in one second. It can process information even within a Pico second. The speed of the computer is affected by various factors such as processor speed, clock cycle, size of RAM, addressing scheme, instruction set, data bus capacity etc. Following term are used to describe the processing power of computer.

v Millisecond: 1/1000 second (10^-3 second).

v Microsecond: 1/1000,000 second (10^-6 second).

v Nanosecond: 1/1000,000,000 second (10^-9 second).

v Pico second: 1/1000,000,000,000 second (10^-12 second).

Storage: They have a large amount of memory to hold a very large amount of data. A large amount of data/information can be stored in secondary storage devices. A computer can store large amount of data in very small space. The storage capacity of compute is virtually unlimited. The data can be stored and retrieved according to the need of user with more ease. It takes a very less time to retrieve the desired data from a huge volume data stored in computer. Hence, the capability of storing and retrieving the huge volume of data in a fast and efficient manner is one of the important characteristics of computer.

Accuracy: Computer’s physical circuits rarely make errors, if the data and instruction are correctly fed. Most of the errors occurring in computers are either hardware errors or human errors. In addition of being fast, computers are very accurate. The accuracy of computer is very high. Error in computer is due to user rather than technological weakness. Computer acts upon the data as per given instructions and then gives the desired output. For instance, if the data we entered is wrong or the instructions we have given are not proper, computer is not going to give desired output.  Computer error caused due to incorrect input data or improper instructions (i.e. unreliable programs) are often called Garbage in, Garbage out (GIGO).

Diligence: It means being constant and earnest in effort and application. It is free from problems like lack of concentration, confusions etc. It is never confused like humans and can consecutively take instructions without failing or getting bored. Computers can work for hours continuously, unlike human being without getting tired. It can work for as many hours, doing the same repetitive without getting bored. Computers are also free form monotony (i.e. its concentration does not fade away after working for several hours). There is no aging effect in computer i.e. efficiency doesn’t decreases over the years of use

Versatility: Many different types of tasks can be performed on computer. At one point of time, it might be busy in calculating statistical data for annual performance evaluation of a business organization and at the other point of time; it might be working on inventory control. Computer can perform various tasks, at different time or simultaneously. At one moment it may doing some massive calculations, the next moment it is busy creating some reports. They can also work with different types of data and information like graphic, audio, visual, characters etc

Programmability: A computer is programmable device, i.e. what it does depend on the lines of instruction (program) it is using.

Power of Remembrance: Unlike humans, computers can store things for unlimited period of time. They have a great remembering power. As human being gains new knowledge, they can retain only 30-40% of knowledge in their memory cells (i.e. brain). Generally the degree of remembering depends upon individual to individual. This means human tends to forget the things over the time. But computer can store and recall any amount of information because of its secondary storage. Every piece of information can be retained as long as required by users.

Non-intelligent: Computer is a dumb machine and it cannot do any work without instruction from the user. It performs the instructions at tremendous speed and with accuracy. It is you to decide what you want to do and in what sequence. So a computer cannot take its own decision as you can. It does not have feelings or emotion, taste, knowledge and experience. Thus it does not get tired even after long hours of work. It does not distinguish between users.

Processing: Computer can process large volume of data in great speed. There are different types of operation during processing such as input/output operation, logic/comparison operation, text manipulation operation etc.

Limitations of Computer (What computer cannot do?)

In spite of above mention characteristics, it does possess some limitations also, which are strength of human beings. These are:

a)      I.Q zero: Computer possesses no intelligence of their own. There I.Q is zero. It cannot catch logical flaws in the program supplied to it. It cannot take its own decision in this regard. It works according to the instruction only.

b)     No feeling: Computer are just the machine, hence has no instincts and no feelings at all. Based on our feeling, taste, knowledge and experience, we often make certain judgment in our day to day life. However, the computer cannot make such judgment themselves. Their judgment is based on the instruction given by the user in the form of programs.

c)      No intuition: Computer cannot draw conclusion without going through all intermediate steps. i.e. they do not have intuition. It can perform only the jobs that can be expressed in finite number of steps. Each step must be clearly defined. The computer is useless without correct programs.

d)   No learning power: Computer has no learning power. Once you give instructions to a computer how to perform a task, the very task is cannot perform if you do not give it any instructions for the next time. For example, when you are taught how to solve a problem and it same type of problem is given to you to solve, then you can do it because you have learned how to solve the problem.

Disadvantages of Computer

1.   It cannot be used on the dusty and the rough environment.

2.   Computer is very expensive so each and every people cannot afford the computer.

3.   Repair and maintenance is required frequently.

4.   Skilled user is required to work inside the computer

5.  Electricity is needed to operate but may be destroyed by electric shock and other physical    destruction.

Computer Organization

A computer organization consists of the combination of input unit, central processing unit (primary storage, Arithmetic and Logic Unit, Control Unit), and output unit together with secondary storage. It is also referred as Computer Architecture. The Central Processing Unit (CPU) is the brain of the computer. The function of CPU is to store temporarily current data and execute programs. The CPU also controls the operations of input and output devices and memory. Under the control of CPU, data and programs are stored in the memory and displayed on the monitor or printed on the printer.

The internal architecture design of computers differs from one system model to another. However, basic organization remains the same for all computer system. A block diagram of the basic computer organization is shown in the following figure.

Figure: Basic Organization of a Computer System

There are three major unit of an electronic digital computer. The units are Input unit, Output unit, and Central Processing Unit (CPU).

Input Unit

It accepts the data or instructions given by the user and it converts the data and instructions from man readable to machine readable code. We can say that input unit links the external environment with the computer system. Some common input devices are keyboard, mouse, scanner, punched card reader, magnetic tape reader, magnetic disk reader etc. Data and instructions are taken in various forms depending on input devices used. For example, data through keyboard entered similar to typing, and this differs from the way in which data is entered through a punched card. However, regardless of the forms in which they accept input, all devices transformed that into binary codes that the primary memory of the computer is designed to accept. This transformation is accomplished by units called input interfaces.

The following functions are performed by an input unit:

ü  It must provide a computer with data and instructions that are necessary to perform the task.

ü  It converts that input data in computer acceptable form i.e. binary code.

ü  It supplies the converted instructions and data to the computer system for further processing which are stored temporarily in RAM.

Output Unit

The function of an output unit is just reverse of that of input unit. Output unit supplies the computed data to the outside world. Thus it links computer with the external environment. As computer work with the binary code, the results produced are also in the binary form. Hence before supplying the results to the outside world, it must be converted to human readable form. This task is accomplished by units called output interfaces. Common output devices are CRT displays, card-punching machines, and magnetic tape drives etc.

The following are performed by an output unit:

ü  It accepts the result produced by the computer which is in binary form.

ü  It converts these coded results to human understandable form.

ü  It supplies the converted results to the outside world.

Central Processing Unit (CPU)

The CPU is the brain of the computer system. In a computer system all major calculations and comparisons are made inside the CPU and the CPU is also responsible for activating and controlling the operations of other units of a computer system. Central processing unit works with operating system and executes a set of instruction and controls different peripheral devices by sending and receiving control signals. The CPU also controls the flow of data by directing the data to enter the system, placing data in the memory, sending the data to ALU for the processing and directing the output of information. The two basic components of a CPU in the above diagram are the arithmetic logic unit and the control unit.

Arithmetic Logic Unit (ALU)

The Arithmetic Logic Unit (ALU) of a computer system is the place where the actual execution of the instructions takes place during the processing operation. In general, all calculations (addition, subtraction, multiplication and division etc.) are performed and all comparisons (decisions) are made in ALU. The data stored in the primary storage are transferred to ALU where processing takes place and intermediate and final results are transferred to storage. The control unit tells the ALU which operation to perform and then see that necessary data to be supplied.

Control Unit

The control unit sequences the operation of the computer, controlling the actions of all other units. That interprets the instructions and then directs the rest of the machines in its operation. Although, it does not perform any actual processing on data, the control unit acts as a central nervous system coordinates the entire computer system.

Storage Unit

The input data, final and intermediate results produced by the computer must be kept somewhere inside the computer system. The storage unit of a computer is designed to fulfill all these needs.

The functions of storage unit are to hold:

ü  All the data to be processed and the instructions required for processing.

ü  Intermediate results of processing.

ü  Final results of processing before these results are released to an output device.

The storage unit of all computers is comprised of the following two types:

Primary Storage

The primary storage, also known as main memory, is used to hold pieces of program instructions and data, intermediate results of processing, and recently produced results of processing. However, the primary storage can hold information only while the computer system is on. As soon as the computer system is switched off or reset, the information held in the primary storage disappears. The primary storage of modern computers systems is made up of semiconductor devices.

Secondary Storage

The secondary storage, also known as auxiliary storage, is used to take care of limitations of the primary storage; it is used to supplement the limited storage capacity and the volatile characteristic of primary storage. Secondary storage is much cheaper than primary storage and it can retain information even when computer system is switched off or rest. The most commonly used secondary storage medium is the magnetic disk

Data and Control Flow

In computer system architecture, we have two types of flow. Data flow is the flow of instructions and data from I/O device to other components. Control flow is the flow of control from control unit to other components.

Uses and Application of Computer

Computer is used in different fields. It is used to solve from day to day activities to complex types of problems related to banking, airlines, educations, health sectors etc. The major applications of computers are given below

1. In Education: Computers are used in schools and colleges as teaching aid. Students can learn their subjects with the help of a computer and take its help to solve different problems related to their subject. In educational field, computers are used in administration and in the area of teaching and learning lessons. In administration computer are used to:

- Keep records of teachers and students.

- Keep accounts of students

- Produce monthly bill statements, salary sheets and mark sheets.

Using multimedia system teachers can present lessons in more understandable and in an organized way. Students also can learn subjects themselves using computers. They can browse internet to get information related to their lessons.

2. In Designing and Engineering: Computers are used for designing clothes, magazines, book covers etc. Engineers use computers to help them create designs of new houses, buildings, bridges, machines, cycles, vehicle etc.

3. In Entertainment: Computers are used to create characters and various animations. They are also used for playing various computer games at home. Computers can be used to watch T.V programs and movies. Audio music can also be played in the computer. In a movie special effects are put with the help of computers to make the movie more realistic and more interesting. Film producers take the help of computers to make cartoon movies and animation films. Music composers use computers for composing music and to set various notes and tunes accurately. In radio stations and FM stations, computers are used to manage and play songs, advertisement etc. Computers are used for creating new notes and rhythm (timing) in music. Musicians use computers to compose and develop music in a much quicker and faster way.

4. In Medical fields: Scientists and doctors take the help of computer in the research and development of new medicines to fight new diseases. In hospitals, computers are used to keep records of patients’ diseases, different medical tests and treatment of diseases. For the diagnosis of diseases, doctors take help of special computer (ECG machine, Ultrasound Machine, CT-Scan machine and others machines). In Intensive Care Unit (ICU) of hospitals, special computers are used to monitor the condition of patients and record the necessary information. Computers are used in hospitals and clinics for carrying out different medical tests. Doctors use computers to keep records of patients for future use. Computers are used to examine the progress of a patient under intensive care.

5. Printing and Publishing: Computers are used for publishing and printing books in various shapes and sizes. Computers help in providing error-free documents for newspapers on time.

6. In Science and Technology: Computers are used in the invention and development of different modern scientific instruments and equipments. Space satellites are linked with computers to control and monitor the proper functioning of airplanes and space equipments. Scientists use computers in different experiments. They use computers in scientific research works and in space research.

7. Transport: Computers are used for seat reservations, control and maintaining timetables of vehicles etc. One can reserve his/her seat from the hotel itself and get it confirmed without having to go to the station or the airport.

8. In Banking field: Computers are used in banks to handle thousands of accounts and calculations of payments receipts, cheques etc. Accounts can be transferred from one place to another from one’s home itself. Bank takes the help of computers for the accurate calculation of payments, interest and balance amount. Nowadays most of the banks provide service of ATM (Automatic Teller Machine) to their customers. Computers are used to control the ATM in banks. The customers can draw money from ATM machines when they insert their ATM cards in the ATM machines.

9. Defense: Computers are used in defense services for monitoring secrets of enemies and different other satellite technology. Computers are also used in the invention and development of new weapons for defense uses. Computers are also used in keeping track of weapons and ammunitions produced and used.

10. In Offices: Computers are used in offices to prepare different kinds of documents. Computers help in keeping records of office employees. Computers also help in sending Electronic mails (email).

11. In Factories: In the big factories computers are used to control machines and tools. Computers are used to control the quality of products. In the factories like car manufacturing factories, aircraft manufacturing factories, microprocessors manufacturing factories and many others factories computer controlled machine ‘ROBOTS’ are used to handle those jobs where it is risky, very sharp accuracy is needed or heavy equipment are to be joined.

12. In Electric Appliances: In homes, tiny computers embedded in the electronic circuitry of most appliances control the indoor temperature, operate home security systems, tell the time, and turn videocassette recorders (VCRs) on and off. Computers in automobiles regulate the flow of fuel, thereby increasing gas mileage, and are used in anti-theft systems.

Types of Computers

We can classify the computer into following broad categories and each category has its own categories given as below:

On the above diagram, we have seen that there are two types of computers: Special purpose and General purpose computers. General purpose computers are the digital computers and special purpose computers are mostly analog and hybrid computers. This classification is according to the working principle or function of the computers. According to the functional style also, we have three types of computers: Analog, Digital and Hybrid computers.

On The Basis of Work

1. Analog Computer

The word “Analog” means continuously varying in quantity. The analog computers accept input data in continuous form and output is obtained in the form of graphs. It means that these computers accept input and give output in the form of analog signals. The output is measured on a scale. The voltage, current, sound, speed, temperature, pressure etc. values are examples of analog data. These values continuously increase and decrease. The analog computers are used to measure the continuous values. The thermometer is an example of analog device because it measures continuously the length of a mercury column. Another example of analog computer is the analog clock because it measures the time by means of the distance continuously covered by the needle around a dial. Similarly, speedometer, tire-pressure gauge are also examples of analog devices.

The analog computers have low memory size and have fewer functions. These are very fast in processing but output return is not very accurate. These are used in industrial units to control various processes and also used in different fields of engineering.

2. Digital Computer

The word “Digital” means discrete. It refers to binary system, which consists of only two digits, i.e. 0 and 1. Digital data consists of binary digits represented by OFF (low) and ON (high) electrical pulses. These pulses are increased and decreased in discontinuous form rather than in continuous form.

In digital computers, quantities are counted rather than measured. A digital computer operates by counting numbers or digits and gives output in digital form. A digital computer represents the data in digital signals, 0 and 1, and then processes it using arithmetic and logical operations. Examples of digital devices are calculators, personal computers, digital watches, digital thermometers etc. Today most of the computers used in offices and homes are digital computers.

The main features of the computers are:

• Give accurate result.
• Having high speed of data processing.
• Can store large amount of data.
• Easy of program and are general purpose in use.
• Consume low energy.

Differentiate between Analog and Digital Computers

Analog Computer	Digital Computer
Accept input data in continuous form and output is measured on a scale.	Accept input data in digital form and output is received in digital form.
It may have some errors in output.	Output is accurate.
Have low internal memory.	Have large internal memory.
Have fewer functions.	Have large number of functions.
It is used only in scientific, industrial and medical fields.	It is general purpose in use.
It is costly.	It is low in cost.
It is not easily programmed.	It is easily programmed.

3. Hybrid Computer

The hybrid computers have best features of both analog and digital computers. These computers contain both the digital and analog components. In hybrid computers, the users can process both the continuous (analog) and discrete (digital) data. These are special purpose computers. These are very fast and accurate. These are used in scientific fields. In hospitals, these are used to watch patient’s health condition in ICU (Intensive Care Unit). These are also used in telemetry, spaceships, missiles etc.

Comparison between Digital, Analog and Hybrid Computer

Digital Computer	Analog Computer	Hybrid Computer
A computer that uses binary digits to display discrete information is called digital computer.	A computer that uses analog signal to display information is called analog computer.	A computer that is able to understand binary as well as analog signal to display information is called hybrid Computers.
Information is in discrete form. It displays information in the form of text, graphics, and pictures.	Information in continuous form and displayed in the form of curves. It is used to measure continuous physical quantity like as current flow, temperatures, blood pressure, heart beats.	Information depends on operating mode of computers. It can display information in discrete and continuous form because its one part is dedicated for digital processing and next part is for analog processing.
Slow	Fast	Intermediate in speed
Accurate	Less  accurate	Intermediate
General purpose	Special purpose	Special purpose
Less  noisy	Noisy	Depend on computer
Use for programming	Not use for programming	Depend on computer
Storage memory	No memory storage	Depend on computer

On the basis of Size

Computers are classified according to their data processing speed, amount of data that they can hold and price. Generally, a computer with high processing speed and large internal storage is called a big computer. Due to rapidly improving technology, we are always confused among the categories of computers.

1. Supercomputer

Supercomputer is the most powerful and fastest, and also very expensive. It was developed in 1980s. It is used to process large amount of data and to solve the complicated scientific problems. It can perform more than one trillion calculations per second. It has large number of processors connected parallel. So, parallel processing is done in this computer. In a single supercomputer, thousands of users can be connected at the same time and the supercomputer handles the work of each user separately. Supercomputer is mainly used for:

• Weather forecasting
• Nuclear energy research
• Aircraft design
• Automotive design
• Online banking
• To control industrial units

Supercomputers are used in large organizations, research laboratories, aerospace centers, large industrial units etc. Nuclear scientists use supercomputers to create and analyze models of nuclear fission and fusions, predicting the actions and reactions of millions of atoms as they interact. The examples of supercomputers are CRAY-1, CRAY-2, Control Data CYBER 205 and ETA A-10 etc.

2. Mainframe Computer

Mainframe computers are also large-scale computers but supercomputers are larger than mainframe. These are also very expensive. The mainframe computer specially requires a very large clean room with air-conditioner. This makes it very expensive to buy and operate. It can support a large number of various equipments. It also has multiple processors. Large mainframe systems can handle the input and output requirements of several thousand of users. For example, IBM, S/390 mainframe can support 50,000 users simultaneously. The users often access then mainframe with terminals or personal computers. There are basically two types of terminals used with mainframe systems. These are:

i) Dumb Terminal

Dumb terminal does not have its own CPU and storage devices. This type of terminal uses the CPU and storage devices of mainframe system. Typically, a dumb terminal consists of monitor and a keyboard (or mouse).

ii) Intelligent Terminal

Intelligent terminal has its own processor and can perform some processing operations. Usually, this type of terminal does not have its own storage. Typically, personal computers are used as intelligent terminals. A personal computer as an intelligent terminal gives facility to access data and other services from mainframe system. It also enables to store and process data locally.

The mainframe computers are specially used as servers on the World Wide Web. The mainframe computers are used in large organizations such as Banks, Airlines and Universities etc. where many people (users) need frequent access to the same data, which is usually organized into one or more huge databases. IBM is the major manufacturer of mainframe computers. The examples of mainframes are IBM S/390, Control Data CYBER 176 and Amdahl 580 etc.

3. Minicomputer

Minicomputers are smaller in size, have lower processing speed and also have lower cost than mainframe. These computers are known as minicomputers because of their small size as compared to other computers at that time. The capabilities of a minicomputer are between mainframe and personal computer. These computers are also known as midrange computers.

The minicomputers are used in business, education and many other government departments. Although some minicomputers are designed for a single user but most are designed to handle multiple terminals. Minicomputers are commonly used as servers in network environment and hundreds of personal computers can be connected to the network with a minicomputer acting as server like mainframes, minicomputers are used as web servers. Single user minicomputers are used for sophisticated design tasks.

The first minicomputer was introduced in the mid-1960s by Digital Equipment Corporation (DEC). After this IBM Corporation (AS/400 computers) Data General Corporation and Prime Computer also designed the mini computers.

4. Microcomputer

The microcomputers are also known as personal computers or simply PCs. Microprocessor is used in this type of computer. These are very small in size and cost. The IBM’s first microcomputer was designed in 1981 and was named as IBM-PC. After this many computer hardware companies copied the design of IBM-PC. The term “PC-compatible” refers any personal computer based on the original IBM personal computer design.

The most popular types of personal computers are the PC and the Apple. PC and PC-compatible computers have processors with different architectures than processors in Apple computers. These two types of computers also use different operating systems. PC and PC-compatible computers use the Windows operating system while Apple computers use the Macintosh operating system (MacOS). The majority of microcomputers sold today are part of IBM-compatible. However the Apple computer is neither an IBM nor a compatible. It is another family of computers made by Apple computer.

Personal computers are available in two models. These are:

1. Desktop PCs
2. Tower PCs

A desktop personal computer is most popular model of personal computer. The system unit of the desktop personal computer can lie flat on the desk or table. In desktop personal computer, the monitor is usually placed on the system unit.

Another model of the personal computer is known as tower personal computer. The system unit of the tower PC is vertically placed on the desk of table. Usually the system unit of the tower model is placed on the floor to make desk space free and user can place other devices such as printer, scanner etc. on the desktop. Today computer tables are available which are specially designed for this purpose. The tower models are mostly used at homes and offices.

Microcomputers are further divided into following categories.

• Laptop computer
• Workstation
• Network computer
• Handheld computer

a. Laptop Computer

Laptop computer is also known as notebook computer. It is small size (85-by-11 inch notebook computer and can fit inside a briefcase. The laptop computer is operated on a special battery and it does not have to be plugged in like desktop computer. The laptop computer is portable and fully functional microcomputer. It is mostly used during journey. It can be used on your lap in an airplane. It is because it is referred to as laptop computer.

The memory and storage capacity of laptop computer is almost equivalent to the PC or desktop computer. It also has the hard dist, floppy disk drive, Zip disk drive, CD-ROM drive, CD-writer etc. it has built-in keyboard and built-in trackball as pointing device. Laptop computer is also available with the same processing speed as the most powerful personal computer. It means that laptop computer has same features as personal computer. Laptop computers are more expensive than desktop computers. Normally these computers are frequently used in business travelers.

b. Workstations

Workstations are special single user computers having the same features as personal computer but have the processing speed equivalent to minicomputer or mainframe computer. A workstation computer can be fitted on a desktop. Scientists, engineers, architects and graphic designers mostly use these computers.

Workstation computers are expensive and powerful computers. These have advanced processors, more RAM and storage capacity than personal computers. These are usually used as single-user applications but these are used as servers on computer network and web servers as well.

c. Network Computers

Network computers are also version of personal computers having less processing power, memory and storage. These are specially designed as terminals for network environment. Some types of network computers have no storage. The network computers are designed for network, Internet or Intranet for data entry or to access data on the network. The network computers depend upon the network’s server for data storage and to use software. These computers also use the network’s server to perform some processing tasks.

In the mid-1990s the concept of network computers became popular among some PC manufacturers. As a result several variations of the network computers quickly became available. In business, variations of the network computer are Windows terminals, NetPCs and diskless workstations. Some network computers are designed to access only the Internet or to an Intranet. These devices are sometimes called Internet PCs, Internet boxes etc. In home some network computers do not include monitor. These are connected to home television, which serves as the output devices. A popular example of a home-based network computer is Web TV, which enables the user to connect a television to the Internet. The Web TV has a special set-top box used to connect to the Internet and also provides a set of simple controls which enable the user to navigate the Internet, send and receive e-mails and to perform other tasks on the network while watching television.

Network computers are cheaper to purchase and to maintain than personal computers.

d. Handheld Computer

In the mid 1990s, many new types of small personal computing devices have been introduced and these are referred to as handheld computers. These computers are also referred to as Palmtop Computers. The handheld computers sometimes called Mini-Notebook Computers. The type of computer is named as handheld computer because it can fit in one hand while you can operate it with the other hand. Because of its reduced size, the screen of handheld computer is quite small. Similarly it also has small keyboard. The handheld computers are preferred by business traveler. Some handheld computers have a specialized keyboard. These computers are used by mobile employees, such as meter readers and parcel delivery people, whose jobs require them to move from place to place.

The examples of handheld computers are:

          i.     Personal Digital Assistance

        ii.     Cellular telephones

      iii.     H/PC Pro devices

i. Personal Digital Assistance (PDAs)

The PDA is one of the more popular lightweight mobile devices in use today. A PDA provides special functions such as taking notes, organizing telephone numbers and addresses. Most PDAs also offer a variety of other application software such as word processing, spreadsheet and games etc. Some PDAs include electronic books that enable users to read a book on the PDA’s screen.

Many PDAs are web-based and users can send/receive e-mails and access the Internet. Similarly, some PDAs also provide telephone capabilities.

The primary input device of a PDA is the stylus. A stylus is an electronic pen and looks like a small ballpoint pen. This input device is used to write notes and store in the PDA by touching the screen. Some PDAs also support voice input.

ii. Cellular Phones

A cellular phone is a web-based telephone having features of analog and digital devices. It is also referred to as Smart Phone. In addition to basic phone capabilities, a cellular phone also provides the functions to receive and send e-mails & faxes and to access the Internet.

iii. H/PC Pro Devices

H/PC Pro dive is new development in handheld technology. These systems are larger than PDAs but they are not quite as large as typical notebook PCs. These devices have features between PDAs and notebook PCs. The H/PC Pro device includes a full-size keyboard but it does not include disk. These systems also have RAM with very low storage capacity and slow speed of processor.

Difference between Minicomputer and Microcomputer

Microcomputer	Minicomputer
A microcomputer is a standard desktop computer used at a home and in business.	Minicomputers are mid-sized computer used in universities, research labs and small corporations.
A microcomputer is a computer with a microprocessor as its CPU.	Minicomputers are faster than microcomputers.
They are cheap, compact and can be easily accommodated on a study table.	They are expensive and larger than microcomputer.
Microcomputer is a single-user computer.	Minicomputer is a multi-user computer.
The two most common types of storage devices used with microcomputers are tapes and disks.	For secondary storage, most minicomputers use magnetic disks or tapes.
Microcomputer is not powerful or as fast as minicomputer.	Minicomputer is powerful than microcomputer but not as super computer and mainframe computer.
Examples are- Modern computers like desktop, laptop etc.	Examples are- IBM 9375, Motorola 68040 etc.

On the Basis of Brand

On the basis of brand, computer has three world wide brands:

1. IBM PC

The IBM (International Business Machine) Personal Computer, commonly known as the IBM PC, is the original version of the IBM PC compatible hardware platform. It is developed by IBM Company.  It is IBM model number 5150, and was introduced on August 12, 1981. It was created by a team of engineers and designers under the direction of Don Estridge of the IBM Entry Systems Division in Boca Raton, Florida.

2. IBM Compatible

A computer which can use hardware and software designed for the IBM PC and its own additional features are called IBM compatible computers.

IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT.

3. Apple computer

The Apple series of micro computers was developed by Steve Wozniak and Steve Jobs in 1976. This used 8-bit microprocessor chips. The chip enabled them to put together a complete computer, a keyboard for input, and processors in memory and screen all in small box. Apple II is known as personal computer. IBM PC and its compatible versions have largest share in PC market. Most of the users of the world have IBM PC, but Macs have its own users, mostly people interested in graphics works and publishing sectors.

On the Basis of Model

On the basis of model, computer is classified as:

1. XT Computer (Extra Technology)

It cannot support GUI based operating system. Its processing speed is 4.77 M Hz and Intel 8080, 8086, 8088 series of microprocessors is used.

2. AT Computer (Advance Technology)

It supports GUI based operating systems. Its speed is 2 G Hz and word length64 bits. Its processors are Intel series of 80286, 80386, 80486, Pentium I, Pentium II etc.

3. PS/2 Computer

It is a laptop computer with rechargeable and battery based system. It is operated with OS/2 operating system.

Detail Types of Computer as per Syllabus

The different types of computer include:

1. Laptop
2. Desktop
3. Palmtop

1. Laptop

Laptop computers are portable devices that use less power and make less noise than desktop models. But, they're often a little slower and have less graphics and sound processing power, although these differences can be too small for most users to notice. Overall, lap­top and desktop computers are very similar. They have the same basic hardware, software and operating systems. The primary difference is how their components fit together.A desktop computer includes a motherboard, video card, hard drive and other components in a large case. The monitor, keyboard, and other peripherals connect wirelessly or with cables. Whether the case sits vertically or horizontally, it has lots of space for add-in cards, cables and air circulation. A laptop, however, is much smaller and lighter than even the most compact PC tower. Its screen is an integrated part of the unit, as is its keyboard. Instead of a spacious case with lots of room for air circulation, a laptop uses a small, flat design in which all the pieces fit together snugly.

Because of this fundamental design difference and because of a laptop's inherent portability, components have to:

·         Fit into a compact space

·         Conserve power

·         Produce less heat than desktop components

Laptop Processors

The CPU or microprocessor works with the operating system to control the computer. The CPU produces a lot of heat, so a desktop computer uses circulating air, a fan and a heat sink -- a system of plates, channels and radiator fins used to draw heat off of the processor -- to cool off. Since a laptop has far less room for each of these cooling methods, its CPU usually:

·         Runs at a lower voltage and clock speed -- This reduces heat output and power consumption but slows the processor down.

·         Mounts to the motherboard without using pins -- Pins and sockets take up a lot of room in desktop PCs. Some motherboard processors mount directly to the motherboard without the use of a socket. These designs save space, but in some cases mean that the processor cannot be removed from the motherboard for replacement or upgrading.

·         Has a sleep or slow-down mode -- The computer and the operating system work together to reduce the CPU speed when the computer is not in use or when the processor does not need to run as quickly.

Some laptops use desktop CPUs that are set to run at lower clock speeds. Although this can improve performance, these laptops typically run much hotter and have a significantly reduced battery life.

Laptop Memory and Storage

A laptop's memory can make up for some of the reduced performance that comes from a slower processor. Some laptops have cache memory on or very near the CPU, allowing it to access data more quickly. Some also have larger busses, allowing data to move between the processor, motherboard and memory more quickly.

Laptops often use smaller memory modules to save space. Memory types used in laptops include:

·         Small Outline Dual Inline Memory Module (SODIMM)

·         Dual Data Rate Synchronous RAM (DDR SDRAM)

·         Single data rate Synchronous RAM (SDRAM)

·         Proprietary memory modules

Figure: SODIMM Module

Some laptops have upgradeable memory and feature removable panels for easy access to the memory modules. Like a desktop, a laptop has an internal hard disk drive, which stores the operating system, applications and data files. However, laptops generally have less disk space than desktops. A laptop hard drive is also physically smaller than that of a desktop. In addition, most laptop hard drives spin more slowly than desktop hard drives, reducing both heat and power consumption.

Desktop computers have multiple bays for installing additional drives, such as CD and DVD ROM drives. However, space in a laptop is in much shorter supply. Many laptops use a modular design, allowing a variety of drives to fit in the same bay. These drives come in three different designations:

·         Hot swappable - The computer can stay on while changing the drive.

·         Warm swappable - The computer can stay on while changing the drive, but the corresponding bus (the path the drive uses to send data to the CPU) must be inactive.

·         Cold swappable - The computer must be off during the swap.

Laptop Screen, Graphics and Sound

A graphics processing unit (GPU) is a microprocessor that handles the calculations necessary for 3-D graphics rendering. Like a CPU, a GPU produces a lot of heat. Most laptops have graphics capability built into the motherboard or have smaller graphics cards with a GPU designed specifically for laptop use. Laptops frequently share memory between the CPU and the GPU, saving space and reducing power consumption.

A laptop displays its graphics on a liquid crystal display (LCD) screen. Most screens measure between 12 and 17 inches, and the size of the screen affects the overall size of the laptop. In addition, laptop screens can be:

·         Black-and-white (16 grayscale) or color (65,536 colors)

·         Active or passive matrix

·         Reflective or backlit

Active matrix displays have sharper images and are easier to read, and backlit screens are better for low-level lighting conditions.

Most laptops also have sound cards or integrated sound processing on the motherboard as well as small, built-in speakers. However, there is generally not enough space inside a laptop for a top-of-the-line sound card or a high-quality speaker.

Laptop Batteries

Laptops ­and desktops both run on electricity. Both have small batteries to maintain the real-time clock and, in some cases, CMOS RAM. However, unlike a desktop computer, a laptop is portable and can run on batteries alone.

·         Nickel-Cadmium (NiCad) batteries were the first type of battery commonly used in laptop computers, and older laptops sometimes still use them. They have a life of roughly two hours between charges, but this life decreases with each charge based on the memory effect.

·         Nickel-Metal Hydride (NiMH) batteries are the bridge between NiCad and the newer Lithium-Ion (LiIon) batteries. They last longer between charges than NiCad but overall have a shorter total lifespan. They suffer from the memory effect, but to a lesser extent than NiCad batteries.

·         LiIon batteries are the current standard for laptop computers. They are light and have long life spans. They do not suffer from the memory effect, can be charged randomly, and won't overheat if overcharged. LiIon batteries can last for anything from about 950 up to 1200 charges.

Many laptops with LiIon batteries claim to have a 5-hour battery life, but this measurement can vary greatly depending on how the computer is used.

2. Desktop

Desktop computers are full-size computers that are small enough to be used at a desk but too big to carry around. These computers consist of hardware, software, and operating systems. In desktop computers, motherboard, hard disk, video card, and other components are assembled into a large case. The monitor, keyboard and other peripherals connect wirelessly or with cables. Currently, desktop computer can have LCD monitor also. LCD monitors come in different size and different features. The case has lots of space for add-in cards, cables and air circulation. The desktop computers are not portable.

In desktop computers, different other devices can be added as mother board has additional slots for devices. For example, additional RAM, hard disk can be added, different CD, DVD drives can be added easily. The desktop computers have slot for printer, scanner, and multimedia projector and also have different number of USB ports where USB port devices like mouse, keyboard, pen drives, etc can be easily used. In order to use printer, scanner driver software of those devices need to be installed.

Now a day's desktop computers uses LCD monitor also but Flat CRT monitors are still available in the market. Desktop computers can be easily networked by installing Network Interface Card (NIC) in the computer as motherboard has slot for NIC.

Present desktop computers are very powerful as they can be used even as server. It has very good display quality. But the major problems with the desktop computers are:

• It occupies ample of space,
• It is not portable, and
• It consumes more electricity and it makes noise in comparison to laptop.

 
3. Palmtop

Many new types of small personal computing devices have been introduced, and all fall under the category of handheld personal computers. These tiny systems are called palmtop computers. PDA is one of the categories of palmtop computers.  

PDAs (Personal Digital Assistants)

PDAs are among the smallest of portable computers. Often, they are no longer than a small appointment book, but they are much less powerful than notebook or desktop computers. The main purpose of a personal digital assistant (PDA) is to act as an electronic organizer or day planner that is portable, easy to use and­ capable of sharing information with your PC. It's supposed to be an extension of the PC, not a replacement.

PDAs have definitely evolved over the years. They can be used to manage your personal information, such as contacts, appointments, and to-do lists, today's devices can also connect to the Internet, act as global positioning system (GPS) devices, and run multimedia software.

Types of PDAs

1. Traditional PDAs: Today's traditional PDAs are descendents of the original PalmPilot and Microsoft Handheld PC devices. Palm devices run the Palm OS (operating system), and Microsoft Pocket PCs run Windows Mobile.

2. Palm PDAs: Most Palm devices are made by palmOne, which offers the Zire and Tungsten product lines. The company formed in 2003 when Palm Computing acquired Handspring, Inc. Sony, which produced the Palm-based CLIE, stopped producing PDAs in 2005. Known for their ease of use, Palm OS PDAs have:

·         A vast library of third-party applications (more than 20,000) that you can add to the system

·         An updated version of the Graffiti handwriting-recognition application

·         Synchronization with both Windows and Macintosh computers using the Palm Desktop

·         Smaller displays than Pocket PCs to accommodate a dedicated Graffiti area on the device

3. Pocket PCs: Pocket PC is the generic name for Windows Mobile PDAs. Their standard features include:

·         Pocket versions of Microsoft applications such as Microsoft Word, Excel, and Outlook

·         Synchronization with Microsoft Outlook on a Windows PC

·         Three handwriting-recognition applications: Transcriber, Letter Recognizer and Block Recognizer

·         A virtual writing area, which maximizes the display size

·         Windows Media Player for multimedia content

4. Smartphones: A smartphone is either a cell phone with PDA capabilities or a traditional PDA with added cell phone capabilities, depending on the form factor (style) and manufacturer. Characteristics of these devices include:

·         A cellular service provider to handle phone service

·         Internet access through cellular data networks

·         Various combinations of cell phone and PDA features, depending on the device    

·         A number of different operating systems, including Windows Mobile Pocket PC Phone Edition, the Palm OS, the Blackberry OS for Blackberry smart phones etc.

PDA Features

Even the most basic PDAs handle standard personal information management (PIM) functions, run application software and synchronize with PCs. Some of the standard PIM functions are as follows:

·         Store contact information (names, addresses, phone numbers, e-mail addresses)

·         Make to-do lists

·         Take notes

·         Track appointments (date book, calendar)

·         Remind you of appointments (clock, alarm functions)

·         Perform calculations

Synchronize With PCs

Because PDAs are designed to complement your PC, they need to work with the same information in both places. If you make an appointment on your desktop computer, you need to transfer it to your PDA; if you jot down a phone number on your PDA, you should upload it later to your PC. Synchronization software on the PDA works with companion software that you install on your PC. Microsoft Pocket PC devices use ActiveSync and Palm OS devices use HotSync synchronization software.

Common PDA Functions

Today, most PDAs incorporate wireless and multimedia functions of some type. Functions found on most (but not necessarily all) devices include:

·         Short-range wireless connectivity using Infrared (IR) or Bluetooth technology

·         Internet and corporate network connectivity through Wi-Fi and wireless access points

·         Support for Wireless WAN

·         A memory card slot that accepts flash media such as CompactFlash, MultiMediaCard, and Secure Digital cards

·         Audio support for MP3 files and a microphone, speaker jack and headphone jack

PDA Battery

PDAs are powered by batteries. Some models use alkaline (AAA) batteries, while others use rechargeable batteries (lithium, nickel-cadmium or nickel-metal hydride). The battery life depends on what kind of PDA you have and how you use it. Here are some of the things that can drain batteries:

·         Operating system (PocketPC requires more power by virtue of its increased memory requirements)

·         More memory

·         Wireless connections, such as Wi-Fi and Bluetooth

·         Backlighting on the display

PDA Display and Input

LCD Display

PDAs use an LCD (liquid-crystal display) screen. Unlike the LCD screens for desktop or laptop computers, which are used solely as output devices, PDAs use their screens for output and input. The LCD screens of PDAs are smaller than laptop screens, but vary in size. Almost all PDAs now offer color displays. PDA displays have the following features:

·         Transflective TFT (thin-film transistor) LCD for indoor and outdoor use

·         Different pixel resolutions with higher resolutions for better quality

·          Color screen

·         Backlighting for reading in low light

Input Methods

PDAs vary in how you input data and commands. Some devices use a stylus and touch screen exclusively in combination with a handwriting recognition program. Using a plastic stylus, you draw characters on the device's display or dedicated writing area. Software inside the PDA converts the characters to letters and numbers. On Palm devices, the software that recognizes these letters is called Graffiti. Graffiti requires that each letter be recorded in a certain way, and you must use a specialized alphabet.

If you can't get the hang of PDA handwriting, you can use a miniature onscreen keyboard. It looks just like a regular keyboard, except you tap on the letters with the stylus. In addition, many devices now include a small (and usually cramped) QWERTY keyboard. Some of these require you to use your thumbs to type.

Central Processing Unit

The central processing unit (CPU) is the brain of the computer system. Among other things, its configuration determines whether a computer is fast or slow in relation to other computers. The CPU is the most complex computer system component, for interpreting and executing most of the commands from the computer's hardware and software. CPU consists of a variety of circuitry and components that are packaged together and connected directly to the motherboard. CPU runs program by fetching instructions from RAM, evaluating them, and executing them in sequence. The instructions are numbers of the binary system, in a special format that is unique for each machine. The CPU breaks an instruction into parts to see if it has to do something. After the CPU determines what an instruction is supposed to do, it tells its component parts what to do to complete the instruction. CPU is usually mounted on the main circuit board, called the motherboard in microcomputer.

The CPU circuitry of a microcomputer, called a microprocessor, fits on a chip about the size of our thumbnail, or even smaller. CPUs are small, square and contain multiple metallic connectors or pins on the underside. The CPU is inserted directly into a CPU socket, pin side down, on the motherboard. Each motherboard will support only a specific type or range of CPU so we must check the motherboard manufacturer's specifications before attempting to replace or upgrade a CPU. As one computer generation has evolved to the next, the size of the CPU has become smaller and smaller, while its speed and capacity have creased tremendously. Indeed, these changes resulted in the microcomputer that is small enough to fit on our desk or our lap.

Most personal computers today use CPUs manufactured by Intel or Advanced Micro Devices (AMD); some examples of their processors are shown in the following figure.

Desktop Processors Typically have 2 to 4 cores and are designed for performance.	Server and Workstation Processors Typically have at least 4 cores and are designed for very high performance.
Notebook Processors Typically have 2 to 4 cores and are designed for performance and increased battery life.	Netbook Processors Typically have 1 to 2 cores, are small in size, and are designed for extended battery life.

 

Figure: CPUs

 

 

 

 

As shown in the figure, there are processors designed for desktop computers, servers and workstations, conventional portable computers (like notebook and tablet computers), and very small portable computers (like netbooks). In addition, there are also processors designed for mobile phones and embedded computers. Many CPUs today are multi-core CPUs; that is, CPUs that contain the processing components or cores of multiple independent processors on a single CPU. For example, dual-core CPUs contain two cores and quad-core CPUs contain four cores. Up until just a few years ago, most CPUs designed for desktop computers had only a single core; as a result, a common way to increase the amount of processing performed by the CPU was to increase the speed of the CPU. However, heat constraints are making it progressively more difficult to continue to increase CPU speed, so CPU manufacturers today are focusing on multi-core CPUs to increase the amount of processing that a CPU can do in a given time period.

Multi-core CPUs allow computers to work simultaneously on more than one task at a time, such as burning a DVD while surfing the Web, as well as to work faster within a single application if the software is designed to take advantage of multiple cores. Another benefit of multi-core CPUs is that they typically experience fewer heat problems than single-core CPUs because each core typically runs slower than a single-core CPU, although the total processing power of the multi-core CPU is greater. In addition to heat reduction, goals of CPU manufacturers today include creating CPUs that are as energy-efficient as possible (in order to reduce power consumption and increase battery life) and that use materials that are not toxic when disposed of.

In addition to computers, CPUs are incorporated into a number of other devices, such as mobile phones, portable digital media players, consumer appliances, cars, gaming consoles, exercise machines, and more. The CPUs for these devices are typically different from the ones used in personal computers.

Factors affecting CPU Performance

The first consideration in selecting a computer is typically its speed: how quickly it can carry out such tasks as loading a program, opening a file, and writing to a CD. Processor manufacturers design a variety of processors to meet numerous needs and budgets.

Processor family	Computer type	Description
Intel Celeron AMD Sempron	Desktop PCs	Manufactured for users on a limited budget; doesn’t support high-end graphics applications
Intel Pentium AMD Athlon, AMD Phenom	Desktop PCs	Moderate multiuse processors for a variety of computer types
Intel Core 2 AMD Athlon X2	Desktop PCs and notebooks	Dual-core and quad-core processors for advanced graphics and high-speed processing
AMD Turion X2	Notebook PCs	Dual-core high performance, low power for long battery life
Intel Itanium AMD Opteron	Servers	Designed for multiple processor computing
Intel Xeon	Workstations	Designed for high-speed processing on special-purpose computers
Intel Core i7	Desktop PCs	Includes “intelligent multi-core for extreme gaming”
Intel Atom	Netbooks and mobile devices	Low power, fast performance, longer battery life

Table: Varying processors for varying needs

When selecting processors for computers, businesses typically consider speed and power consumption. One component that contributes to the speed at which a processor can carry out an instruction is the system clock. Each CPU contains a system clock that produces a series of electronic pulses at a predetermined rate called the clock speed. These pulses are used to synchronize processing activities. Just as a person’s heartbeat circulates blood through the body, the system clock distributes bits and bytes through the components of a computer system. Clock speeds in today’s digital devices are measured in megahertz (MHz), millions of cycles per second, or gigahertz (GHz), billions of cycles per second. Faster clock speeds generate more heat in a device and require larger cooling systems. For this reason, we’ll find that smaller devices generally have a lower maximum available clock speed.

Although clock speed has a direct effect on overall system performance, it is not the only contributing factor. In fact, clock speeds can be deceptive. Some older computers might have faster clock speeds but perform much slower than today’s computers. This is because today’s smarter architectures, such as multicore architectures, are able to do much more with each cycle of the system clock. In today’s computers, it is not so much how fast the system clock ticks, but how much the processor can do with each tick of its clock.

Rather than emphasizing clock speed when marketing its processors, Intel uses processor numbers. For example, one model of the Intel Core2 Extreme processor is processor number QX6800. The processor number represents performance specifications that contribute to system performance. The following table lists these factors.

Architecture	Basic design of a microprocessor; may include process technology and/or other architectural enhancements
Cache (MB/KB)	A temporary storage area for frequently accessed or recently accessed data; having certain data stored in a cache speeds up the operation of the computer. Cache size is measured in megabytes (MB) or kilobytes (KB).
Clock speed (GHz/MHz)	Speed of the processor’s internal clock, which dictates how fast the processor can process data; clock speed is usually measured in GHz (gigahertz, or billions of pulses per second)
Front side bus (GHz/MHz)	The connecting path between the processor and other key components such as the memory controller hub; FSB speed is measured in GHz or MHz

Table: Computer performance factors

Cache (pronounced cash) memory is a type of high-speed memory that a processor can access more rapidly than RAM. Cache memory functions somewhat like a notebook used to record phone numbers. Although a person’s private notebook may contain only 1 percent of all the numbers in the local phone directory, the chance that the person’s next call will be to a number in his or her notebook is high. Cache memory works on the same principle: a cache controller makes “intelligent guesses” as to what program instructions and data are needed next and stores them in the nearby cache for quick retrieval.

Three levels of cache are used in today’s personal computers: L1, L2, and L3. The levels indicate the cache’s closeness to the CPU. L1 is stored on the same chip as the microprocessor; L2 and L3 are on separate chips. Considerably more expensive than RAM, cache memory is provided in much smaller capacities. Cache sizes vary from processor to processor. The larger the cache, the faster the processing.

Another important factor that affects a computer’s performance is the processor’s wordlength. Wordlength is the number of bits that a CPU can process at once. A processor with a 32-bit wordlength has the capacity to be twice as fast as a processor with a 16-bit wordlength. Today’s personal computers typically use wordlengths of 32 or 64 bits. Intel Pentium 4 processors have a 32-bit wordlength; AMD Athlon 64 processors have a wordlength of 64 bits. The benefits of 64-bit wordlength are only experienced if the operating system and software are designed to take advantage of the processor’s 64-bit capabilities. While Intel processors and both Windows and Mac OS X have evolved to 64-bit architectures, software developers have been slower to migrate their applications from 32-bit to 64-bit. That is likely to change as 64-bit processors become the norm.

By now we’ve gathered that judging a computer’s quality and speed by its specifications can be complicated. The truest measure of a processor’s performance is the amount of time it takes to execute an instruction. This measure is called MIPS, for millions of instructions per second; a more precise measurement is called FLOPS, for floating-point operations per second. Today’s personal computers carry out billions of instructions per second, or operate in the gigaflop range. Supercomputers run in the teraflop (trillion) and peta flop (quadrillion) range. For example, IBM’s ASCI White computer assists the U.S. government in simulating a nuclear detonation at 12.3 teraflops—12.3 trillion floating-point operations per second. It has been estimated that a human brain’s probable processing power is around 100 teraflops, roughly 100 trillion calculations per second. The fastest supercomputer in 2009, according to the “top 500” ranking (www.top500.com), was the IBM Roadrunner, which was clocked at 1.1 petaflops. The next-generation IBM Sequoia is being designed to run at 20 petaflops.

Components of CPU

CPU consists of three primary components: the arithmetic logic unit, the control unit, and registers.  The parts of the CPU are usually connected by an electronic component referred to as a bus, which acts as an electronic highway between them.

 

 

 

 

 

 

 

 

 

 

 

                                       Figure: Block Diagram of CPU

1. Arithmetic Logic Unit (ALU)

Without the arithmetic/logic unit (ALU), computers would not be able to do most of the tasks that we find useful. The ALU performs all the arithmetic and logical (comparison) functions, that is, it adds, subtracts, multiplies, divides, and does comparisons. These comparisons, which are basically "less than," "greater than," or "equal to," can be combined into several common expressions, such as "greater than or equal to," The objective of most instructions that use comparisons is to determine which instructions should be executed next.

Many instructions carried out by the control unit involve simply moving data from one place to another- from memory to storage, from memory to the printer, and so forth. When the control unit encounters an instruction that involves arithmetic or logic, however, it passes that instruction to another component of the CPU, the arithmetic logic unit, or ALU.

The ALU controls the speed of calculations and so receives a great deal of attention from computer engineers trying to meet the needs of the fast-paced business world. Older microcomputers' speeds are usually measured in milliseconds (l thousandth of a second). Newer, powerful computers' speeds are measured in nanoseconds (1 billionth of a second) or picoseconds (l trillionth of a second).

Function of ALU

l  It accepts operands from registers.

l  It performs arithmetic and logical operations.

l  It returns results to register or a memory.

l  The status of an ALU operation (negative, carry, zero, overflow) is available for writing into Flags register (FL).

Arithmetic Operations	Logical Operations
+  Add	=, ¹  equal to, not equal to
-  Subtract	>, ≯  greater than, not greater than
X  Multiply	<, ≮   less than, not less than
¸  Divide	³,  ≱ greater than or equal to, not greater than or equal to
^  Raise by a power	£, ≰ less than or equal to,  not less than or equal to

Table: Operations Performed by the Arithmetic Logic Unit

2. Control Unit

The control unit, a maze of complex electronic circuitry, is responsible for directing and coordinating most of the computer system activities.  The CPU's instructions for carrying out commands are built into the control unit. The instructions, or instruction set, list all the operations that the CPU can perform. Each instruction in the instruction set is expressed in microcode -a series of basic directions that tells the CPU how to execute more complex operations. It determines the movement of electronic signals between the main memory and the arithmetic/logic unit, as well as the control signals between the CPU and input/output devices. It controls the entire operation of the computer and manages all the computer’s resources.

Just as a car is useless without gas, a computer is not much good without software instructions. When we use software, we are working with high-level (human language-like) instructions that are to be carried out by the control unit. These instructions are converted by a language processor into a low-level form of instructions the computer can work with - machine language, the only language that the CPU can understand. In machine language, data and instructions are represented in binary form (0s and 1s), and each type of computer - microcomputer, minicomputer, or mainframe responds to a unique version. Once the instructions have been converted into this form, they can be retrieved from main memory and interpreted by the control unit (sometimes referred to as decoding). According to each specific instruction, control unit issues the necessary signals to other computer system components as needed to satisfy the processing requirements. This could involve, for example, directing that data be retrieved from a disk storage device, "telling" the printer to print the letter you just wrote, or simply directing the arithmetic/logic unit to add two numbers.

The functions of control unit are:

1. It sends the input from the input device to the primary memory
2. Then, the raw data is send to the ALU for processing
3. It interprets the instructions in the program.
4. It then sends back the processed data from the ALU to the memory.
5. Finally it sends the meaningful information from the primary memory to the output unit.
6. The control unit repeats a set of four basic operations: Fetching, Decoding, Executing and Storing

 

3. Registers

Register are special temporary storage locations within the CPU. They hold various types of information such as data, instructions, addresses, and the intermediate results of calculations when ALU performs arithmetic and logical operations. Registers very quickly accept, store, and transfer data and instructions that are being used immediately. To execute an instruction, the control unit of the CPU retrieves it from main memory and places it into a register.

The number and types of registers in a CPU vary according to the CPU's design. Their size (capacity) and number can dramatically affect the processing power of a computer system. In general, the "larger" the register (the more bits it can carry at once), the greater the processing power. Some personal computers have general purpose registers that hold only 8 bits; others hold 16 bits; newer microcomputer have 32-bit registers. The difference in processing power is due to difference in register size.

Most of the conventional modern computers are based upon the "stored program computer" concept which is credited to the mathematician John Von (1903-1957). The following figure illustrates the machine structure of CPU for a typical Von Neumann machine (IBM system /360).

Figure: Machine Structure

The structure of CPU above consists of:

-        An Instruction Interpreter

-        A location counter

-        An Instruction Register

-        A Working Register and a General Register

Instruction Interpreter:- The instruction interpreter is a group of electrical circuits that performs the intent of instructions fetched from memory.

Location Counter (LC):- The Location Counter (LC), also called Program Counter (PC) or Instruction Counter (IC), is a hardware memory device that denotes the location of the current instruction being executed.

Instruction Register (IR):- A copy of the current instruction is stored in the instruction Register (IR).

Working Register and General Register:- The working registers are memory devices that serve as "scratch pads" for the instruction interpreter because they are used to store temporary values while calculation is in progress, while the general registers are used by the programmer as storage locations and for special functions.

The primary interface between the memory and the CPU is via the memory address register and the memory buffer register. The Memory Address Register (MAR) contains the address of the memory location that is to be read from or stored into. The Memory Buffer Register (MBR) contains a copy of the designated memory location specified by MAR after a “READ”, or new contents of the memory location prior to a “WRITE”. The memory controller is hardware that transfers data between MBR & the core memory location the address of which is in the MAR.

The role of I/O Channels is to input or output information from memory.

Bus and Its Type

A collection of wires through which data is transmitted from one part of a computer to another is known as Bus. The term bus usually refers to internal bus of a computer system. It is also known as communication pathway, which connects all the internal computer components to the CPU and main memory and I/O devices. In other words, the bus is the channel, which lets the parts of a computer, to communicate with each other.

There is also an expansion bus that enables external devices, such as the keyboard, mouse, modem, printer, etc., to access the CPU and memory. Cables from disk drives and some other internal devices may also be plugged into the bus. The size of a bus, known as its width, determines how much data can be transmitted at one time. Buses transfer data in parallel. In 16-bit bus, data are sent over 16 wires simultaneously. Every bus has a clock speed measured in MHz. The wider the bus, the more data it can carry at one time, and thus the greater the processing speed of the computer.

The ALU, the control unit and the primary storage unit must have a way to communicate. These links among and within the various units are called buses. For example, the control bus is the pathway for all timing and controlling functions sent by the control unit to the other units of the system. The address bus is the pathway used to locate the storage position in memory where the next instruction to be executed or the next piece of data will be found. The data bus is the pathway where the actual data transfer takes place. The three bus paths are shown in the following figure.

	Address Bus

 

Figure: Communication Pathways/ Buses within a Computer

A bus is classified by name according to its function.

Control Bus

Control bus is the physical connection that carries control information between the CPU and other devices within the computer. The control bus consists of 4 to 10 parallel signal lines that report the status of various devices. It is the path for all timing and controlling functions sent by the control units to other units of the system. The CPU sends out signals on the control bus to enable the outputs of addressed memory devices or port devices. Typically control bus signals are: Memory Read/Write, and I/O Read/Write.

Address Bus

Address bus is a channel which transmits addresses of data (not the data) from the CPU to memory. The address bus connects only the CPU and RAM and carries only memory addresses. The address bus consists of 16, 20, 24, or 32 parallel signal lines. The number of lines (wires) in the address bus determines the amount of memory that can be directly addressed as each line carries one bit of the address. If the CPU has N address lines, then it can directly address 2^N address lines.  For example, a computer with a 32-bit address bus can directly address 4GB of physical memory, while one with 36 bits can address 64GB. However, the actual amount of memory that can be accessed is usually much less than this theoretical limit due to chipset and motherboard limitations.

Data Bus

Data bus is a channel across which actual data are transferred between the CPU, memory, and I/O devices. The data bus consists of 8, 16, 32, or 64 parallel signal lines. Because each wire can transfer 1 bit of data at a time, an 8-wire bus can move 8 bits at a time, which is a full byte. A 16-bit bus can transfer 2 bytes, and a 32-bit bus can transfer 4 bytes at a time. The number of wires in the bus affects the speed at which data can travel between hardware components, just as the number of lanes on a highway affects how long it takes people to reach their destinations. The wider the data bus, the more data it can carry at one time. It is one of the main factors determining the processing power of a computer. Most current processor designs use a 32-bit bus, meaning that 32 bits of data can be transferred at once. The data bus is bidirectional, this means that the CPU can read data in from memory or it can send data out to memory.

Common Bus Technologies

PC buses are designed to match the capabilities of the devices attached to them. When CPUs could send and receive only 1 byte of data at a time, there was no point in connecting them to a bus that could move more data. As microprocessor technology improved, however, chips were built that could send and receive more data at once, and improved bus designs created wider paths through which the data could flow. Common bus technologies include:

• The Industry Standard Architecture (lSA) bus is a 16-bit data bus. ISA became the de facto industry standard on its release in the mid-1980s and is still used in many computers to attach slower devices (such as modems and input devices) to the CPU.

• Local bus technology was developed to attach faster devices to the CPU. A local bus is an internal system bus that runs between components on the motherboard. Most system buses use some type of local bus technology today and are coupled with one or more kinds of expansion bus.

• The Peripheral Component Interconnect (PCI) bus is a type of local bus designed by Intel to make it easier to integrate new data types, such as audio, video, and graphics.

• The Accelerated Graphics Port (AGP) bus incorporates a special architecture that allows the video card to access the system's RAM directly, greatly increasing the speed of graphics performance. The AGP standard has led to the development of many types of accelerated video cards that support 3-D and full-motion video. While AGP improves graphics performance, it cannot be used with all PCs. The system must use a chip set that supports the AGP standard. Most new computers feature AGP graphics capabilities in addition to a PCI system bus and an expansion bus.

• Two new expansion bus technologies promise to replace most existing buses in the future. These bus types- Universal Serial Bus (USB) and IEEE 1394 (called FireWire on Macintosh computers)- not only provide fast data transfer speeds, they also eliminate the need for expansion slots and boards. Most new PCs and Macintosh computers feature at least one USB port, and each USB port can support 127 different devices. If you have USB- compliant devices such as keyboards, mice, printers, and modems, you can plug them all into a single USB port.

Traditionally, the performance of computer buses was measured by the number of bits they could transfer at one time. Hence, the newest 64-bit buses are typically considered the fastest available. However, buses are now also being measured according to their data transfer rates- the amount of data they can transfer in a second. This type of performance is usually measured in megabits per second (Mbps) or megabytes per second (MBps).

For example, a USB bus has a data transfer rate of 12 Mbps. An IEEE 1394 bus has a data transfer rate of 400 Mbps. AGP buses are typically rated at 266 MBps but can support data transfer rates of more than 1 GBps. PCI buses offer data transfer rates of 133 MBps.

Some manufacturers also rate the speed of their system buses in megahertz. For years, system buses ran at a speed of 66 MHz; contemporary systems offer bus speeds of 100 MHz and 200 MHz. When coupled with a fast processor, a high-speed bus can result in an exceptionally high-performance system. 

 
Storage (Memory)

Introduction

If a business cannot store data and information, it cannot work - or not. In a non-computerized office, data is stored temporarily in in-boxes and out-boxes, and semi-permanently in file cabinets and on microfilm. In a computerized information processing environment, data is stored in a form that is directly usable by the computer for processing, that is, in computer-usable form. Storage can be temporary, such as in the transaction file, or semi-permanent, as in the master file.

As you can imagine, the cost of managing huge amounts of paper documents and their storage areas can be overwhelming -- both in a monetary sense and in a personnel management sense. Indeed, this cost is often the main reason for a business to switch to a computer-based information system. Computer-based storage is:

1. Economical. It takes up far less space than paper documents.
2. Secure. With the use of storage controls, data is usually safe from unauthorized users, and with the use of backup systems that duplicate data for storage in a second location, data is also safe from natural and people-made disasters.
3. Almost unlimited. There is virtually no limit to the amount of data that can be stored off-line.

Why is Storage an Important concept?

Not understanding the concept of computer storage is like not understanding the concept of a car’s gasoline tank. Without using a gasoline tank, you would not be able to get your car to go very far because, of course, without tank, you cannot use gasoline. Similarly, if you do not use a storage device with your computer, you would not have the capability to store the data that will make your computer useful.

In general, data is stored in a computer system for three principal reasons. First, current input data needs to be held for processing. For instance, the sales order data is input and stored temporarily in a transaction file until the need arises to produce invoices. Second, some types of data are stored on a relatively permanent basis and retrieved as required during processing. For example, to produce a customer invoice, you need data from the customer file: customer's name, address, billing instructions, and terms. Third, data is stored to be periodically updated. In our case, after the invoices have been produced, the accounts receivable file (reflecting what customers owe) needs to be updated to reflect the latest purchases. In addition to all this data, the computer software instructions must be stored in a computer-usable form because a copy of the software must be read into the main memory from a storage device before data processing can begin.

As you rise in the organizational world, you will very likely be required to write reports for your supervisor or manager. Picture yourself sitting down in front of a microcomputer for the first time with the intent of creating a report for your boss. Before you can begin, you must determine where the software that you will use to write the report is stored. Once you have written your report, you will need to save a copy of it on a storage device (particularly if you do not finish it in a single sitting). To do these things, you have to know about storage. Also, if you are going to create a very large report, the capacity of your storage medium and device may be a consideration. For example, depending on your particular computer system and the storage devices connected to it, a 100-page document may not fit on one diskette. How, then, do you write your report?

Also, to know what kind of computer system to request to buy, you need to be familiar with the differences in speed, cost, and capacity of various types of storage devices.

Storage Fundamentals

Storage hardware provides the capability to store data and program instructions, either temporarily or permanently, for quick retrieval and use during computer processing. Since we are comparing computer systems to humans from the beginning, memory is also no exception. As human memory is made up of cells (neurons), computer memory is also made up of large number of cells. Here, each cell is capable of storing one bit of information in the form of binary numbers.

Memory in a computer system is required for the storage and subsequent retrieval of instruction and data. A computer system uses variety of devices for storing instructions and data required for its operations. Normally, the information to be stored on computer is classified in two basic categories-- data and instructions.

The storage device along with the algorithm or information on how to control and manage these storage devices constitutes the memory system of computer. Although a memory system is a very simple system yet it exhibits a wide range of technology and types. But unfortunately, faster memory technology is more costly. In addition, fast memories require power supply till information is stored. These things are not very convenient. But, on the other hand, memories with smaller cost have very high access time. This is the time taken by CPU to access a location in memory. This results in slower operation of CPU. Thus, the cost versus access time has led to a hierarchy of memory where we supplement fast memories with larger, cheaper and slower memories. The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. The memory unit may have different physical and operational characteristics. Therefore, memory system may have different types, costs, organizations, technologies and performances. This memory hierarchy will be fruitful if the frequency of access to slower memories is significantly less than the faster memories.

							Cache
								Main Memory (RAM)
									Magnetic Disk
									Magnetic Tape

 

Figure: Memory Hierarchy

Thus, a memory system can be considered to consist of two groups of memories. These are as follows:

1. Primary memory or main memory

2. Secondary or auxiliary memory

Primary Memory or Main Memory

The term primary storage refers to the main memory of a computer, where both data and instructions are held for immediate access and use by the computer's central processing unit during processing. CPU continuously reads instructions stored and executes from main memory. It is the working space used by the computer to hold the program that is currently running, along with the data it needs to process.

Although the technology is changing, most primary storage today is considered a volatile form of storage, meaning that the data and instructions are lost when the computer is turned off. This temporary storage is also known as main memory or simply memory. It is faster, expensive and small in size relative to the secondary memory.

Primary memory is made up of cells. The cells are small storage area in primary memory. Cells have fixed length means they can store only fixed number of bits called word length of that particular primary storage. Each cell has a unique address. The size of memory is generally measured in some power of 2. The capacity of the main memory is measured in Kilobytes (KB) or Megabytes (MB) or Gigabytes (GB).

Primary memory is accessed by CPU in random fashion, This means that each element of memory is directly accessible and can be examined and modified without affecting other cells. Physically, it consists of some chips either on the motherboard or on a small circuit board attached to the motherboard of a computer. It is attached to the processor via its address and data buses.

The primary storage section is used for four purposes, out of which three are related to data processing.

ü  Data are fed into an input storage area where they are held until ready to be processed.

ü  A working storage space, that is like a sheet of paper, is used to hold the data being processed and the intermediate results of such processing.

ü  An output storage area holds the finished results of the processing operations until they can be released.

ü  In addition to these data related purposes the primary storage section also contains a program storage area that holds the processing instructions.

Disadvantage of Primary Memory

ü  The primary memory is volatile in nature.

ü  The cost per unit of storage is very high for the primary memory.

ü  The design of computer generally limits the maximum possible size of primary memory.

Storage Evaluation Criteria

Property	Desirable	Primary Storage	Secondary Storage
Storage Capacity	Large storage capacity	Small	Large
Access Time	Fast access time	Fast	Slow
Cost per bit of storage	Lower cost per bit	High	Low
Volatility	Non- volatile	Volatile	Non-volatile
Access	Random access	Random access	Pseudo-random access or sequential access

Difference between Primary Memory and Secondary Memory

S.N.	Primary Memory	Secondary Memory
1.	It is a semiconductor memory.	It is a magnetic and optical memory.
2.	In memory hierarchy, it is placed in highest position due high speed, high cost and small size.	In memory hierarchy, it is placed in lower position due to low speed, low cost and large size.
3.	Its storing capacity is small.	Its storing capacity is very large.
4.	Processor directly accesses primary memory.	Processor does not directly access secondary memory. It is accessed through I/O interface or I/O Processor.
5.	Example: RAM, ROM	Example: Floppy, ZIP- Floppy, Hard Disk, CD-ROM, VCD, WORM

The Primary memory is further divided into three categories. They are:

a. Cache Memory

b. Random Access Memory (RAM)

c. Read Only Memory (ROM)

a. Cache Memory

A CPU spends lots of its program execution time in either fetching instructions and data or storing results in the primary memory. Hence, the speed with which a CPU can execute a program depends on the speed of the memory. The problem of speed mismatch between CPU and primary memory can be overcome by having a high speed memory, known as cache memory. It is present as an interface between the CPU and the primary memory. It is an optional memory and may not be present in all computers. It is not directly accessible to the users but CPU can access it direct.

Cache (pronounced cash) memory is similar to RAM, except that it is extremely fast compared to normal memory and it is used in a different way. Cache memory is a small memory that resides between the CPU and RAM whose access time is closer to the processing speed of the CPU. The cache speeds processing by storing frequently used data or instructions in its high-speed memory. When a program is running and the CPU needs to read data or program instructions from RAM, the CPU checks first to see whether the data is in cache memory. If the data is not there, the CPU reads the data from RAM into its registers, but it also loads a copy of the data into cache memory. The next time the CPU needs that same data, it finds it in the cache memory and saves the time needed to load the data from RAM.  In the figure, external (Level-2) cache is shown, but most computers also have internal (Level-l) cache memory circuitry built into the CPU.

                                       Figure: Working of Cache Memory

The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. The advantage of cache memory is that the CPU does not have to use the motherboard's system bus for data transfer. The CPU retrieves data or instruction more quickly from cache memory than it does from RAM or a disk.

Cache memory is sometimes described in levels of closeness and accessibility to the CPU. Cache built into the CPU itself is referred to as Level l (Ll) cache. The first L1 caches came with 0.5 KB, then 8 KB, then 16 KB, then 32 KB. Today, many CPUs have as much as 256 KB built in. In addition to the cache memory built into the CPU, cache is also added to the motherboard. Cache that resides on a separate chip next to the CPU is called Level 2 (L2) cache. Many PCs sold today have 512 KB or 1024 KB of motherboard cache memory; higher-end systems can have as much as 2 MB of L2 cache.  Some CPUs have both Ll and L2 cache built-in and designate the separate cache chip as Level 3 (L3) cache.

The successful retrieval of requested data from the cache is known as cache hit. The larger the cache, the more chance that a particular file will be in cache. A failure to find requested data in the cache is known as cache miss. This means the slower memory must be searched to find instruction, the more cache miss, the slower the computer will operate.

b. RAM (Random Access Memory)

Memory that can be instantly changed is called read-write memory or random-access memory (RAM).It is a high speed memory that holds a copy of the operating system, currently executing programs, and other information being processed. It can be written to and read from at any time. It is random because any of the bits and bytes resident in RAM can be accessed non-sequentially. However, the information stored in the RAM is temporary and volatile because the moment another program is fed in it, the initial program stored in that memory location gets erased. The data in RAM stays there only as long as your computer is on, and electricity is flowing through the machine. The information stored on the RAM gets wiped off when the power supply is turned off, Increasing RAM improves system performance. RAM is the most common type of memory found in computers and other devices, such as printers.

RAM has the following characteristics:

ü  Data within the RAM can be read or modified, i.e. you can either read from the RAM or write onto it. Hence it is called read/write memory.

ü  The contents of the RAM are lost when the computer is switched off. Hence, the RAM is said to be volatile.

Figure: RAM

The capacity of RAM can vary from 640 KB to 4 GB and more, depending on the manner of memory chips installed, which in turn depends on the capacity the microprocessor can handle. The RAM size is an important parameter in determining the size and complexity of problems that a computer can handle. When people refer to the amount of memory that a computer has, they are talking about the amount of RAM available.

Memory is installed in memory module slots located on the motherboard. These slots are easily locatable by looking for the small hinges on either side that lock the memory in place. Certain sizes of modules may need to be installed in certain slots so always check with your motherboard manufacturer before purchase or installation.

A computer’s motherboard is designed in a manner that the memory capacity can be enhanced by adding more memory chips. The additional RAM chips, which plug into special sockets on the motherboard, are known as Single In-line Memory Modules (SIMMs). Moving on the next logical step was the DIMMs (Double In-line Memory Modules). The advent of the DIMMs brought with it new speeds and sizes to give computers more power than ever before. The big advancement in recent years has been the introduction of DDR RAM (Double Data Rate). The other big memory type of the recent time is RAMBUS memory. RAMBUS memory uses a memory module called a RIMM (RAMBUS In-line Memory Module). RIMMs are special high speed memory chips working up to 800 MHz. They require special motherboard support and are priced higher than that of standard memory modules.

Types of RAM

The most common form of RAM in use today is built from semiconductor integrated circuits, which can be either static (SRAM) or Dynamic (DRAM).

SRAM (Static Random Access Memory)

SRAM is a type of RAM that does not need to be refreshed as often and retains a value as long as power is supplied. This memory is made up of flip-flops and it stores a bit as a voltage. Each memory cell requires six transistors; therefore, the memory chip has low density but high speed. Since they retain information for longer of time, they are used as cache memory. SRAM is also considerably faster than DRAM. Most DRAM technologies support access times of around 60 nanoseconds. Faster SRAM chips support access times of around 10 nanoseconds. Consequently, SRAM is more expensive and consumes more power than DRAM and is not used as frequently in PCs

DRAM (Dynamic Random Access Memory)

Dynamic RAM is the more common type. Dynamic RAM (DRAM) gets its name from the fact that it must be refreshed frequently. (The term refreshing means recharging the RAM chips with electricity.) This memory is made up of MOS transistors gates and it stores the bit as a charge. The advantages of DRAM are that it has high density, low power consumption and cheaper than SRAM. The disadvantage is that the charge (Bit information) leaks; therefore, DRAM chips must be recharged many times each second, or they will lose their contents. Hence, DRAM is slow compared to DRAM.

Difference between Static RAM (SRAM) and Dynamic RAM (DRAM)

S.N.	Static RAM (SRAM)	Dynamic RAM (DRAM)
1.	Static RAMs hold information in a flip-flop circuit consisting six transistors which is needed in each memory cell. It is a costlier RAM	It requires less number of transistors per memory cell because information is stored in stray capacitors. Only one transistor is needed to form a memory cell of the dynamic RAM. It is a less costly than SRAM.
2.	Its speed is high.	Its speed is lower than SRAM.
3.	It occupies large space.	Small space is occupied by DRAM.
4.	It consumes less power than DRAM.	More power is consumed.
5.	Refresh circuit is not need.	Refresh circuit is needed.

Few other types of RAM

Synchronous Dynamic RAM (SDRAM)

The SDRAM is the newest RAM type. Its speed is synchronous meaning that it is directly dependent on the clock speed of the entire system. Synchronous Dynamic RAM is designed mainly to operate with stability at higher bus speeds such as 100MHz. It has an access time of only 8-12 ns. The advantage of SDRAM is the increased speed. It uses a pipelined design to cope up with speed of CPU. Pipelining enables the SDRAM to accept commands at the same time as it is processing other commands. So this kind of RAM has better performance as data can be read or accessed with much greater speed.

Video RAM

Video RAM is specialized RAM which is used on video cards. Video RAM is dual-ported, which means it can be accessed by two different devices simultaneously. This enables data to be read from video RAM (i.e. sent to the computer monitor) at the same time data is written to video RAM.

Non-Volatile RAM (NVRAM)

NVRAM is a type of RAM that retains its information even when the power is turned off. It is a small 24 pin DIP (Dual Inline Package) integrated circuit chip and is thus able to obtain the power needed to keep it running from the CMOS battery installed in motherboard. It keeps track of various system parameters such as serial number, Ethernet MAC (Media Access Control) address, Host ID, date of manufacturer, etc. NVRAM is therefore a type of non-volatile memory that offers random access.

c. ROM (Read Only Memory)

Read Only Memory cannot be written by the user i.e. a user can only read information stored in it. It contains pre-written instructions related to the operating system of a computer. The combination of hardware and programs written permanently in the ROM chips is called firmware. There are permanently printed in the ROM chips by the manufacturer and the data in this area cannot be edited or removed. It is designed to perform a specific function. The memory capacity of ROM varies from 64 KB to 256 KB depending on the model of computer.

The ROM contains permanently recorded instructions that are vital for starting up a computer. One set of instructions found in ROM is called the ROM-BIOS, that stand for Read Only Memory Basic Input Output System. These programs perform the most basic control and supervisory operations for the computer. For example, they check whether the I/O devices have been connected properly to the system unit. They also handle the basic needs of the hardware involved, which include all input and output devices. Any set of programs residing in ROM is called firmware.

ROM chips are non-volatile because they retain their stored contents even when the electric power is switched off. Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs.

Types of ROM

ROM is mainly of three types. They are:

1. PROM (Programmable Read Only Memory)

2. EPROM (Erasable Programmable Read Only Memory)

3. EEPROM (Electrically Erasable PROM)

1. PROM (Programmable Read Only Memory)

Programmable Read Only Memory is a memory chip on which data can be written only once. PROM is a way of allowing a user to tailor a microcode program using a special machine called a PROM programmer. This machine supplies an electrical current to specific cells in the ROM that effectively blows a fuse in them. The process is known as burning the PROM. Once the operations are written into a PROM chip, they cannot be changed and remains there forever. Unlike the main memory, PROMs retain their contents when the computer is turned off.

The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or a PROM burner. It is useful for companies, which makes their own ROMs for their software. For small quantities, it is cheaper than ROM.

2. EPROM (Erasable Programmable Read Only Memory)

Erasable Programmable Read Only Memory is programmable read only memory that can be erased and re-used. EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light.

A glass window is installed in the top of the ROM package, through which you can actually see the chip that holds the memory. Ultraviolet light of a specific frequency is shined through this window for a specified time period to erase the EPROM and allow it to be reprogrammed again. The EPROM is configured or reconfigured using an EPROM programmer. EPROM’s are mainly used by R & D personnel (experimenters) because they frequently change the micro programs to test the efficiency of the computer system with new programs.

An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROMs are used widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped. This means that bugs can be removed and new versions installed shortly before delivery.

3. EEPROM (Electrically Erasable PROM)

Electrically Erasable PROM is user-modified read only memory that can be erased and reprogrammed (written to) repeatedly with special electrical voltages. Unlike EPROM chips, EEPROM's do not need to be removed from the computer to be modified. When a new program or data needs to be written on it, selective programming can be done to an EEPROM chip. The user can alter the value of certain cells without needing to erase the programming on other cells. Thus, sections of data can be erased and replaced without needing to alter the rest of the chip’s programming. EEPROM has a limited life- that is, the number of times it can be programmed is limited to tens or hundreds or thousands of times.

EEPROM is similar to flash memory (sometimes called flash EEPROM). The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster.

Flash Memory

Flash memory is a special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. These memory chips can be erased and programmed at least a million times. Many modern PCs have their BIOS (Basic Input Output System) stored on a flash memory chip so that it can easily be updated if necessary. Such a BIOS is sometimes called flash BIOS. When BIOS needs to be changed (rewritten), the flash memory can be written in block sizes rather than byte sizes, making it easier to update. Flash memory is also called flash RAM.

Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized. Many applications include PDAs (Personal Digital Assistant), laptops, digital audio players, digital cameras and mobiles uses flash memory.

Regardless of the type of ROM chip used, they all serve to increase the efficiency of a CPU by controlling the performance of a few specialized tasks.

Memory Type	Write Time	Order of Read Time	Number of Cycles allowed
ROM	Once	Nano seconds	One
PROM	Hours	Nano seconds	One
EPROM	Minutes	Nano seconds	Hundreds
EEPROM	Milli-seconds	Nano seconds	Thoudands

Comparison of PROM, EPROM and EEPROM

S.N.	PROM	EPROM	EEPROM
1.	It stands for Programmable ROM.	It stands for Erasable Programmable ROM	It stands for Electrically Erasable Programmable ROM. It is also called EAPROM ( Electrically Alterable PROM)
2.	It is a programmable ROM. Its contents cannot be erased.	Information stored can be erased in ultra violet exposure.	Its contents can be erased by electricity and again it can be programmed like as EPROM.

Difference between RAM and ROM

S.N.	RAM	ROM
1.	It stands for Random Access Memory. It is also called read/write or volatile memory, because its contents can be emptied when refresh command is executed or computer shut down.	It stands for Read Only Memory. It is called dead store, Field Store, Permanent stores and non-volatile memory.
2.	Its contents lost if power is off.	It retains contents if power is off.
3.	RAM is divided into two categories: (a) Static RAM and (b) Dynamic RAM	ROM is also divided into (a) PROM (b)EPROM (c) EEPROM and (d) Flash Memory
4.	Costly or expensive	Cheap in price

Secondary or Auxiliary Memory

The primary storages are used to store only those instructions and data which are to be used primarily. They have limited capacity because the cost pet unit of storage is high. Also they are volatile in nature, meaning that data stored in it is lost when the electric power is turned off or interrupted. However, the computer has to store a large amount of information. So, secondary storage is used for this purpose.

Secondary storage, also known as auxiliary memory or auxiliary storage, is the memory that supplements the main storage. This is a long-term, non-volatile memory. Secondary storage is designed to retain data and instructions (programs) in a more permanent form. Secondary storage is nonvolatile, meaning that the data and instructions remain intact when the computer is turned off. Unlike RAM which looses the contents when the computer is turned off and ROM to which it is not possible to add anything new, auxiliary storage device allows a computer to record information semi-permanently. This is to ensure that this information can be read later by the same computer or by another computer.

Auxiliary storage devices are also useful in transferring data or programs from one computer to another. They are much larger in size than main memory but are slower. These cannot be accessed directly by processor. They also function as backup devices which allows backup of the valuable information that you are working on. So, even if by some accident your computer crashes and the data in it is unrecoverable mode, you can restore it from your backups. The data stored in secondary storage can be stored for the desired time, i.e. they hold information until it is deleted or overwritten. They trade slower access rates for greater storage capacity and data stability and are less expensive. Auxiliary storage is also known as external storage. The most common types of auxiliary storage devices are magnetic tapes, magnetic disks, floppy disks and hard disks.

There are two types of auxiliary storage devices. This classification is based on the type of data access-- sequential and random. Based on the type of access, they are called sequential access media and random media. In case of sequential access media, data stored in media can only be read in sequence. To get to a particular point on media, you have to go through all the preceding points.

Magnetic tapes are examples of sequential access media. In contrast, disks are random access media, also called direct access media, because a disk drive can access any point at random without passing through intervening points. Other examples of direct access media are magnetic disks, optical disks, zip disks etc.

Most widely used secondary storage devices are magnetic tapes, magnetic disk (Hard disk, floppy disk), optical disk (CD, DVD) and flash drive.

Magnetic Tape

Magnetic tape is one of the most popular sequentially access storage mediums for large data. Magnetic tape was the first magnetic mass storage devices. Magnetic tape is a magnetically coated strip of plastic on which data can be encoded. It is used for recording analog or digital data. Tapes for computers are similar to the tapes used to store music. Some personal computers, in fact, enable one to use normal cassette tapes. The tape drive is an input/output device that reads, writes and erases data on tapes. Magnetic tapes are erasable, reusable and durable. Magnetic tape is not suitable for data files that are revised or updated frequently because it stores data sequentially. It is still been used by some banks to take backup.

Storing data on tapes is considerably cheaper than storing data on disks. Tapes also have large storage capacities, ranging from a few hundred kilobytes (KB) to several gigabytes (GB). Accessing data on tapes, however, is much slower than accessing data on disks. Tapes are sequential-access media, which means that to get to a particular point on the tape, the tape must go through all the preceding points. In contrast, disks are random-access media because a disk drive can access any point at random without passing through intervening points.      

Figure: Magnetic Tape

Because tapes are so slow, they are generally used only for long-term storage and backup. Data to be used regularly is almost always kept on a disk. Tapes are also used for transporting large amounts of data.

Tapes are sometimes called streamers or streaming tapes. Tapes come in a variety of sizes and formats which are described in the table given below:

Type	Capacity	Description
Half-inch	60 MB- 400 MB	Half-inch tapes come both as 9 track reels and as cartridges. These tapes are relatively cheap, but require expensive tape drives.
Quarter- inch	40 MB- 5 GB	Quarter-inch cartridges (QIC tapes) are relatively inexpensive and support fast data transfer rates. QIC mini cartridges are even less expensive, but their data capacities are smaller and their transfer rates are slower.
8-mm Helical- scan	1 GB – 5 GB	8-mm helical-scan cartridges use the same technology as VCR tapes and have the greatest capacity. But they require expensive tape drives and have relatively slow data transfer rates.
4-mm DAT	2 GB – 24 GB	DAT (Digital Audio Tape) cartridges have the greatest capacity but they require expensive tape drives and have relatively slow data transfer rates.

Advantages of Magnetic Tapes

·      Storage capacity is virtually unlimited because as many tapes as required can be used for storing very large data sets

·      Cost per bit of storage is very low for magnetic tapes

·      Tapes can be erased and reused many times

·      Tape reels and cartridges are compact and light in weight

·      Easy to handle and store

·      Very large amount of data can be stored in a small storage space

·      Compact size and light weight

·      Magnetic tape reels and cartridges are also easily portable from one place to another

·      Often used for transferring data and programs from one computer to another that are not linked together.

Limitations of Magnetic Tapes

·    Due to their sequential access nature, they are not suitable for storage of those data that frequently require to be accessed randomly.

·    Must be stored in a dust-free environment because specks of dust can cause tape-reading errors.

·    Must be stored in an environment with properly controlled temperature and humidity levels

·    Tape ribbon may get twisted due to warping, resulting in loss of stored data

·    Should be properly labeled so that some useful data stored on a particular tape is not erased by mistake

Uses of Magnetic Tapes

·      For applications that are based on sequential data processing

·      Backing up of data for off-line storage

·      Archiving of infrequently used data

·      Transferring of data from one computer to another that are not linked together

·      As a distribution media for software by vendors

Magnetic Disk

An alternative to tape storage is magnetic disk storage. The two primary types of disks in use are floppy disks and hard disks. The general characteristics and operations of both types are the same. A magnetic disk offers high storage capacity, reliability, and the capacity to directly accessing stored data. Magnetic disks hold more data in a small place and attain faster data access speed. Input signals, which may be audio, video, or data, are recorded on the surface of a disk as magnetic patterns or spots in spiral tracks by a recording head while the disk is rotated by a drive unit. The head is also used to read the magnetic impressions on the disk. Data can be recorded and erased on a magnetic disk any number of times. Types of magnetic disks include diskettes, hard disks, and removable disk cartridges.

A disk is basically a plotter that has been coated with a magnetic material, or, reflective material, in the case of optical disks. Like tape drives, disk drives are equipped with read/write heads. As the disk spins inside the drive, the read/ write head passes over the surface of the disk. A magnetic disk is a thin, circular metal plate/ plotter coated on both side with a magnetic material, it is very similar in appearance to a LP gramophone record.

Information is recorded on the tracks of a disk surface in the form of invisible tiny magnetic spots. The presence of a magnetized spot represents a 1 bit and its absence represents a 0 bit. A standard binary code, usually 8-bit EBCDIC, is used for recording data. In some systems, the outer tracks contain more bits than the inner track. However in most systems, each track contains the same number of characters, which means that the outer tracks of the disk are less densely packed with character than those towards the centers.

Illustrates the concept of Tracks	Illustrates the concept of Sectors

Figure: Magnetic Disk – Storage Organization

 

No. of disk platters= 4, No. of usable surfaces = 6.

A set of corresponding tracks on all the 6 surfaces is called a cylinder.

Figure: Magnetic Disk – Storage Organization (Illustrates the concept of Cylinder)

The more disk surfaces a particular disk pack has, the greater will be its storage capacity. But the storage capacity of the disk systems also depends on the tracks per inch of surface and the bits per inch of track.

Storage capacity of a disk system= Number of recording surfaces * Number of tracks per surface * Number of sectors per surface * Number of bytes per surface

An important factor in measuring overall system performance is the speed at which the computer’s disk drives operate. When evaluating the performance of common storage devices, we need to be aware of disk access time. Disk access time is the interval between the instant a computer makes a request for transfer of data from a disk system to the primary storage and the instant this operation is completed. Disk access time depends on the following three parameters:

-Seek Time: It is the time required to position the read/write head over the desired track, as soon as a read/write command is received by the disk unit.

-Latency: It is the time required to spin the desired sector under the read/write head, once the read/write head is positioned on the desired track.

- Transfer Rate: It is the rate at which data are read/ written to the disk, once the read/write head is positioned over the desired sector

As the transfer rate is negligible as compared to seek time and latency,

Average access time = Average seek time + Average latency

Advantages of Magnetic Disks

• More suitable than magnetic tapes for a wider range of applications because they support direct access of data
• Random access property enables them to be used simultaneously by multiple users as a shared device. A tape is not suitable for such type of usage due to its sequential-access property
• Suitable for both on-line and off-line storage of data
• Except for the fixed type Winchester disks, the storage capacity of other magnetic disks is virtually unlimited as many disks can be storing very large data sets.
• Due to their low cost and high data recording densities, the cost per bit of storage is low for magnetic disks.
• An additional cost benefit is that magnetic disks can be erased and reused many times.
• Floppy disks and zip disks are compact and light in weight. Hence they are easy to handle and store.
• Very large amount of data can be stored in a small storage space
• Data transfer rate for a magnetic disk system is normally higher than a tape system
• Magnetic disks are less vulnerable to data corruption due to careless handling or unfavorable temperature and humidity conditions than magnetic tapes.

Limitations of Magnetic Disks

• Although used for both random processing and sequential processing of data, for applications of the latter type, it may be less efficient than magnetic tapes.
• More difficult to maintain the security of information stored on shared, on-line secondary storage devices, as compared to magnetic tapes or other types of magnetic tapes.
• For Winchester disks, a disk crash or drive failure often results in loss of entire stored data. It is not easy to recover the lost data. Suitable backup procedures are suggested for data stored on Winchester disks.
• Some types of magnetic disks, such as disk packs and Winchester disks, are not so easily portable like magnetic tapes.
• On a cost-per-bit basis, the cost of magnetic disks is low, but the cost of magnetic tapes is even lower.
• Must be stored in a dust-free environment.
• Floppy disks, zip disks and disk packs should be labeled properly to prevent erasure of useful data by mistake

Uses of Magnetic Disks

• For applications that are based on random data processing
• As a shared on-line secondary storage device. Winchester disks and disk packs are often used for this purpose.
• As a backup device for off-line storage of data. Floppy disks, zip disks and disk packs are often used for this purpose.
• Archiving of data not used frequently, but may be used once in a while. Floppy disks, zip disks and disk packs are often used for this purpose.
• Transferring of data and programs from one computer to another that are not linked together. . Floppy disks and zip disks are often used for this purpose.
• Distribution of software by vendors. Originally sold software or software updates are often distributed by vendors on floppy disks and zip disks.

Floppy Disk

Floppy disk is a soft magnetic disk. It is called floppy because it flops if you wave it (atleast the 5¼ inch variety does). Unlike most of the hard disks, floppy disks (often called floppies or diskettes) are portable because these can be removed from a disk drive. Disk drives for floppy disks are called floppy drives. Floppy disks are slower to access than hard disks and have less storage capacity but are less expensive and are portable.

A diskette actually consists of two parts: a plastic disk coated with magnetic material, and a protective plastic jacket or hard shell. The magnetic coating itself is visible through the openings in the jacket of 5.25 inch diskette. But in 3.5 inch diskette the spring loaded shutter covers the opening. The hole in the center called hub ring of the disk, goes round the drive motor, which spins the disk so that the data can be written or read. A small hole near the central hole is called index hole. There is an also a write protect notch on the disk cover, which can be set so that the disk can be prevented from accidental change or erasure of data and virus infection.

Originally the diskette was 8" square. This disk was used in mainframe computers. But 5.25" sq. disk and 3.5" sq. disk are the most common. Each disk has two sides: 0 and 1. The disk is divided into sectors and tracks. A disk may have 40 tracks or 80 tracks and 9, 10,15,18,26 sectors. As the number of sectors or tracks increased the capacity of disk also increases. 5.25 sq. disks are called minidisk and 3.5" sq. disk are called micro disk. The capacity of a disk can be obtained by using following relation.

Disk Capacity = No. of Surfaces x No. of Tracks x No. of Sectors/ Track x No.  of Bytes/Sector

Following are the two basic sizes of a floppy:

1. 5¼ inch-- This is the common size floppy for PCs made before 1987. This type of floppy is generally capable of storing between l00K and 1.2MB of data. The most common sizes are 360K and 1.2MB.

A 5¼ -inch floppy disk enclosed within jacket. The drive mechanism clamps on to a portion of the disk exposed by the drive access opening in the jacket

Figure: 5¼ -inch floppy disk

2. 3¼ inch-- Floppy is something of a misnomer for these disks as they are encased in a rigid envelope. Despite their small size, microfloppies have a large storage capacity than their cousins-- from 400K to 1.4MB of data. The common sizes for PCs are 720K (double density) and 1.44MB (high density). Macintoshes support disks of 400K, 800K and 1.2MB.

             Figure: 3¼ -inch floppy disk

As numbers of floppy disks are available and one can be differentiated from another by means of following factors:

ü  Number of recording surfaces

ü  Storage capacity

ü  Density

ü  Size

Different types of Floppy Disks and their storage capacities are listed below:

Size (Diameter in inches)	Type	No. of surfaces	No. of tracks	No. of sectors/ track	Sectors	No. of bytes/ sector	Capacity in bytes	Approximate capacity
5.25	Double density (DD)	2	40	9	720	512	3,68,640	360 KB
5.25	High density (HD)	2	80	15	2400	512	12,28,800	1.2 MB
3.5	Double density (DD)	2	40	18	1440	512	7,37,280	720 KB
3.5	High density (HD)	2	80	18	2880	512	14,74,560	1.44 MB
3.5	Extra-high density (ED)	2	80	36	5760	512	29,49,120	2.88 MB

The three most common uses of floppy disks are listed below:

1. Moving Files between Computers That Are Not Connected Through Network or Communications Hardware. One of the easiest ways to move data between computers is to copy the data to a floppy disk, remove the floppy disk from the first computer's drive, and insert it in another computer's drive.
2. Loading New Programs onto a System. Although large programs are often delivered on CD-ROM, many programs are still sold on floppy disks. When you buy a program from a software retailer, you install it by copying the contents of the floppy disks onto your hard disk drive or by running a small program on the diskettes that installs the files on your hard drive automatically.
3. Backing Up Data or Programs. The primary copy of data or programs is stored on a hard disk drive. Backing up is the process of creating a duplicate set of programs and/or data files for safekeeping. Because diskettes provide limited storage capacity, they are most often used to back up small groups of data files rather than programs or the entire hard disk.

Hard Disk

Hard disk is the most common storage device for all computers. Hard disk is the storage medium within the computer that stores and provides relative quick access to large amount of data. The term hard is used to distinguish it from a soft, or floppy, disk. Hard disks hold more data and are faster than floppy disks. A hard disk, for example, can store anywhere from 10 MB to several GB whereas most of the floppies have a maximum store capacity of 1.4 MB.

A hard disk is a set of stacked (piled up) 'disks' called platters made up of aluminum material that are coated with iron-oxide on both sides. The disk is permanently sealed in a metal case due to the sensitive operation they perform; the presence of even a small dust particle can destroy the hard disk.

Figure: Hard Disk Drive

A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently. The platters are spaced several millimeters apart and the head floats just above the disk surface to eliminate wear and tear. Each platter has the same number of tracks and n^th track of each platter taken together is called a cylinder. For example, a typical 84 MB hard disk for a PC might have two platters (four sides) and 1,053 cylinders.

Each surface of each disk is divided into a number of evenly spaced concentric circular tracks. Each track is divided into sectors. Each sector of hard disk generally stores 512 bytes of data. The hard disk found in most PCs spin between 3600 rpm (revolution per minute) and 7200 rpm. Some new high-performance hard disk can spin as fast as 10,000 rpm.

The computation of a hard disk's capacity is identical to that for floppy disks, but the numbers are larger-in some cases, much larger. Here is how we would break down the capacity for an extremely large (50 GB) hard disk, assuming that the disk has eleven platters, 264,528 tracks, and about 369 sectors per track:

12,024 cylinders x 22 heads (sides) = 264,528 total tracks

264,528 tracks x 369 average sectors/track = 97,610,823 sectors

97,610,823 sectors x 512 bytes/sector = 49,976,745,984 bytes (approximately)

The total number of bytes is approximate because this simple calculation is based on the average number of sectors per track. (Recall that many hard drives have varying numbers of sectors per track, so an average may be used.) If the actual number of sectors per track were taken into account, the calculation would be more difficult and the resulting number of bytes would be somewhat higher.

Today's computer typically comes with a hard disk that contains several billions byte (gigabyte) of storage space. Hard disk provides faster access to data than floppy disk and capable of storing much more information because platters are rigid, they can be stacked so that one hard disk drive can access more than one platter. Most hard disk has two to eight platters.

In spite of all capacity and speed advantage, hard disks have one major drawback. To achieve optimum performance, the read/write head must be extremely close to the surface of the disk without actually touching the disk. In fact, the read/write heads fly so close to the surface of the disk that if a human hair, a dust particle or even a finger print were placed on the disk, it would bridge the gap between the head and the disk and cause the head to crash. A head crash, in which the head touches the disk, can destroy the data stored in the area of the crash. A severe head crash not only damages the surface of the disk, but it can also destroy a read/write head.

Hard disks are of three types depending on how they are packaged. They are:

1. Zip/ Bernoulli Disks
2. Disk Packs
3. Winchester Disks

Zip/ Bernoulli Disks

Zip disk uses a single hard disk platter encased in a plastic cartridge. Disk drives may be portable or fixed type. Fixed type is part of the computer system, permanently connected to it. Portable type can be carried to a computer system, connected to it for the duration of use, and then can be disconnected and taken away when the work is done. Zip disks can be easily inserted/ removed from a zip drive just as we inset/ remove floppy disks in a floppy disk drives. They are slightly larger than the conventional floppy disks and are about twice as thick. They can hold 100MB of data. Because they are relatively inexpensive and durable, they have become a popular media for backing up and for transporting large files.

Disk Packs

Disk Pack uses multiple (two or more) hard disk platters mounted on a single central shaft. Disk drives have a separate read/write head for each usable disk surface (the upper surface of the top-most disk and the lower surface of the bottom most disk is not used). Disks are of removable/ interchangeable type in the sense that they have to be mounted on the disk drive before they can be used, can be removed and kept off-line when not in use.

Winchester Disks

Winchester Disk uses multiple (two or more) hard disk platters mounted on a single central shaft. Hard disk platters and the disk drive are sealed together in a contamination-free container and cannot be separated from each other. For the same number of disks, Winchester disks have larger storage capacity than disk packs because all the surfaces of all the disks are used for data recording and they employ much greater precision of data recording, resulting in greater data recording density. These disks are named after the .30-30 Winchester rifle because the early Winchester disk systems had two 30-MB disks sealed together with the disk drive.

Comparison of Floppy Disk and Hard Disk

• A floppy disk contains a single, flat piece of plastic (the disk), coated with iron oxide and enclosed in a vinyl or plastic cover. A hard disk contains one or more rigid metal platters, coated with iron oxide, which are permanently encased in the hard disk drive.
• Floppy Disks are small and portable (they can be removed from diskette drives), but hard disks are usually built into the computer, so they are not portable (unless the entire computer is). Built-in hard disk drives cannot be moved easily from one computer to another. There are many different standards in use for hard drives, and the user must make sure that the computer can recognize the hard drive before the two can be used together. Exceptions are removable hard drives and external hard drives, which can simply be detached from the system.
• Most floppy disks store only 1.44 MB, although special floppy disks offer higher capacities. New hard disks can store several thousand times as much data as a floppy disk.
• Hard disk drives are much faster than floppy disk drives; their disks spin faster and they can locate data on the disk's surface in much less time.

Pen Drive

Pen drive is a portable USB flash drives (sometimes called USB flash memory drives, thumb drives, or jump drives) consist of flash memory media integrated into a self-contained unit that connects to a computer or other device via a standard USB port and is powered via the USB port. Universal Serial Bus (USB) is a standard that allows a wide array of devices to connect to a computer through a common port. Although they are called drives, they contain no moving parts as do magnetic or optical drives. They use solid-state technology (devices that store data using transistors) to store data. Pen drives are designed to be very small and very portable. These devices can be used to transfer audio, video, and data files from the hard drive of one computer to another. These drives functions as a portable hard disk. The pen drive derives its name from the fact that many of these USB drive devices resemble a small pen or pencil in size and shape.

In order to appeal to a wide variety of users, pen drives are available in a range of sizes, colours, and appearances—including those designed to be attached to backpacks or worn on a lanyard around the neck; those built into necklaces, wristbands, or wristwatches; those thin enough to fit easily into a wallet; and those made into custom shapes for promotional or novelty purposes.

Conventional Pen Drives	Pen Drive Wristbands	Pen Drive Wallet Cards

Figure: Pen Drives

Pen Drives are plug-and-play portable storage devices that use flash memory and are lightweight enough to attach to a key chain. To read from or write to a pen drive, you just plug it into a USB port. If the pen drive is being used with a computer, it is assigned a drive letter by the computer, just like any other type of attached drive, and files can be read from or written to the pen drive until it is unplugged from the USB port. Although pen drives do not come close to CD-RWs and DVD+RWs in terms of cost per MB, the convenience they offer makes them well worth the expense. The capacity of most pen drives today ranges from 1 GB to 64 GB. Pen drive use has become commonplace for individuals, students, and employees to transport files from one computer to another, as well as to quickly back up important files.

In addition to providing basic data storage and data portability, pen drives can provide additional capabilities. For instance, they can be used to lock a computer and to issue Web site passwords; they can also include biometric features—such as a built-in fingerprint reader—to allow only authorized individuals access to the data stored on the pen drive or to the computer with which the pen drive is being used.

As pen drives grow in capacity and capability, they are threatening the future of magnetic hard drives as the first choice for secondary storage in PCs. Many companies are now producing solid-state disks (SSD) using flash technology to replace the traditional magnetic hard drive in PCs. An SSD reads data 300 percent faster and writes data 150 percent faster than traditional hard drives. It boots up a computer much faster, is lighter and more durable, uses less power, and runs cooler and quieter than a hard drive. SSDs are being used in small notebook PCs designed for business travellers. For example, the MacBook Air offers a 128 GB SSD option. Since it is a relatively new technology, SSD drives are unable to provide the capacity of traditional hard drives, and cost considerably more.

Memory Card

One of the most common types of flash memory media is the memory card (sometimes called a flash memory card or a storage card) —a small card containing one or more flash memory chips, a controller chip, other electrical components, and metal contacts to connect the card to the device or reader with which it is being used. Memory cards are available in a variety of formats, such as Compact Flash (CF), Secure Digital (SD), Secure Digital High Capacity (SDHC), Secure Digital Extended Capacity (SDXC), Multi Media Card (MMC), xD Picture Card (xD), and Memory Stick (MS). These formats are not interchangeable, so the type of memory card used with a device is determined by the type of flash media card that device can accept.

Memory Card Readers Can be built-in or external and usually support several different types of flash memory media; external readers such as this one typically connect to a computer via a USB port.
	Compact Flash (CF) Cards	Memory Sticks
	XD Picture Cards	Secure Digital (SD) Cards

Figure: Memory Cards

Memory cards are the most common type of storage media for digital cameras, portable digital media players, mobile phones, and other portable devices. They can also be used to store data for a personal computer, as needed, as well as to transfer data from a portable device to a computer. Consequently, most desktop and notebook computers today come with a memory card reader capable of reading memory cards; an external memory card reader (that typically connects via a USB port and is shown in the figure) can be used if a built-in reader is not available. The capacity of memory cards is continually growing and is up to about 4 GB for standard cards and 32 GB for high-capacity cards; the even higher capacity extended capacity cards are just beginning to become available and are expected to reach capacities of 2 TB by 2014.

One of the most widely used types of memory media—Secure Digital (SD)—is available in different physical sizes, as well as in different capacities. For instance, standard-sized SD cards are often used in digital cameras and computers; the smaller miniSD and microSD (about one-half and one-quarter the size of a standard SD card, respectively, as shown in the figure) are designed to be used with mobile phones and other mobile devices. When more storage space is needed, higher capacity miniSDHC and microSDHC cards can be used. MMC cards and memory sticks are also available in mobile sizes; adapters can be used with mobile-sized memory cards in order to use them in a full-sized memory card reader.

While general purpose memory cards can be used for most applications, there are also memory cards designed for specific uses. For instance, professional memory cards designed for professional photographers are faster and more durable than consumer cards; gaming memory cards are specifically designed for gaming consoles and devices, such as the Nintendo Wii or Sony PSP; and netbook memory cards are designed to be used to expand the storage capabilities of a netbook computer. There are even Wi-Fi-enabled memory cards that can wirelessly upload digital photos taken with a camera using that card for storage.

Typically, memory media is purchased blank, but some memory-based software (such as games, encyclopedias, and language translators) is available. A new option for portable music is slotMusic—music albums that come stored on microSD cards. These cards can be used with any phone or portable digital media player that has a microSD slot and they typically contain extra storage space to add additional files as desired. Movies are also beginning to be delivered via memory media. In fact, Panasonic and Disney have announced plans to begin releasing movies on microSD cards by 2010 and Sonic Solutions has announced movies stored on USB flash drives should begin to become available at about the same time. These new options for portable multimedia are geared toward individuals who would like access to this content via a mobile phone, car navigation system, netbook, or other device often used while on the go that has a flash memory card slot or a USB port.

Optical Disks

Optical disks are a storage medium from which data is read and to which it is written by lasers. These disks consist of a circular disks, which are coated with a thin metal or some other material that is highly reflective. A very fine laser beam is projected on the reflective surface to read data from the disk. By detecting the light intensity reflected from the surface, the information stored on the disk can be accessed. As optical disks make use of laser beam technology for recording/reading of data on the disk, these disks are also known as laser disk or optical laser disk.

The storage organization of optical disk is quite different than the magnetic disk. There is a difference in track patterns on optical and magnetic disks. Optical disk has one long spiral track, which starts at the outer edge and spirals inward to the center. The track is divided into equal size sectors.

Track Pattern on an optical disk	Track Pattern on a magnetic disk

Figure: Difference in track patterns on optical and magnetic disks

The storage capacity of an optical disk is given by:

Storage capacity of an optical disk= Number of sectors x Number of bytes per second

Optical disks proved to be a promising random access medium for high capacity secondary storage because they can store extremely large amounts of data in a limited space. The optical disks are commonly used for video and audio application because of their various advantages. It is compact, lightweight, durable and digital. It also provides a minimum of 650 megabytes (MB) of data storage. A double-layered and double-sided DVD optical disk holds up to 15.9 gigabytes (GB) of data and dual-layer Blu-ray can store up to 50 GB.

Access Mechanism of Optical Disk

The optical disk drive reads 0s and 1s from a spinning disk by focusing a laser on the disk's surface. Some areas of the disk reflect the laser light into a sensor, and other areas scatter the light. A spot that reflects the laser beam into the sensor is interpreted as a 1, and the absence of a reflection is interpreted as a 0.

Data is laid out on a optical disk drive in a long, continuous spiral that starts at the outer edge and winds inward to the center. Data is stored in the form of lands, which are flat areas on the metal surface, and pits, which are depressions or hollows. A land reflects the laser light into the sensor (indicating a data bit of 1), and a pit scatters the light (indicating a data bit of 0).

Figure: How an optical disk drive reads data from an optical disk

Optical Disk Drive

Optical disk drive uses laser beam technology for reading/writing of data. It has no mechanical read/write access arm. It uses a constant linear velocity (CLV) encoding scheme, in which the rotational speed of the disk varies inversely with the radius.

Figure: Optical Disk Drive

The various types of optical disks used today are CD, DVD, Blu-ray etc.

1. CD (Compact Disk)

A compact disc (CD) is a small, portable, round medium made of molded polymer for electronically recording, storing, and playing back audio, video, text, and other information in digital form. It is a rotating disk which is coated with a thin metal or other material that is highly reflective. Focusing a laser beam (12MW) on the surface of the spinning disk does data recording. The process of recording/writing data to the optical disk is called burning. In order to read the stored data, a less powerful laser beam (5 MW) is focused on the disk surface.

Initially, CDs were read-only, but newer technology allows users to record as well. Standard CDs have a diameter of 120 mm and can hold up to 80 minutes of audio. There is also the Mini CD, with diameters ranging from 60 to 80 mm; they are sometimes used for CD singles, storing up to 24 minutes of audio. Now-a-days compact disks are very popular storage devices for microcomputers because a large number of software including multimedia, audio and graphics software are available on these disks.

Figure: Compact Disk

Some variations of the CD in use today are:

- CD-ROM  (CD – Read Only Memory): These devices are packaged as shiny, silver colour metal disk of 5¼ inch (12 cm) diameter, having a storage capacity of about 650 MB. Like audio CDs, CD-ROMs come with data already encoded onto them. The data is permanent and can be read any number of times but CD-ROMs cannot be modified. Pre-stamping or pre-recording of data by their suppliers on the disk is known as mastering.

- CD-R (CD- Recordable): CD-R is also called Write-Once Read-Many (WORM). Data can be written only once on them, but can be read many times.  After that the CD-R disk behaves just like a CD­ROM.  Data to be recorded can be written on its surface in multiple recording sessions. Sessions after the first one are always additive and cannot alter the etched/burned information of earlier sessions.

- CD-RW(CD- Read/Write): Optical disks that can be erased and loaded with new data, just like magnetic disks. These are often referred to as “Erasable Optical” disks.

- Video CD: Video CD (VCD) is a standard digital format for storing video on a Compact Disc. VCDs are playable in dedicated VCD players.

2. DVD (Digital Video/Versatile Disk)

DVD is an optical disc technology with a 4.7 GB or8.5 GB, which is enough for a 133-minute movie. DVD closely resembles a CD or compact disk. The major difference is that the DVD holds far more data. A CD commonly has a capacity of 650 megabytes, while the smallest capacity DVD can store about seven times more data, or 4.7 gigabytes (GB). DVD is designed primarily to store and distribute movies as it is capable of storing large data. DVD allows storage of video in 4:3 or 16:9 aspect-ratios in MPEG-2 video format using NTSC or PAL resolution. Audio is usually Dolby ® Digital (AC-3) or Digital Theater System (DTS) and can be either monaural or 5.1 Surround Sound.

DVD encodes data in the form of a spiraling trail of pits and lands separated by mere nanometers. The trail starts at the center of the DVD and winds around countless times until it reaches the outer edge. In the case of a double layer disk, the trail continues on a second layer of material. If the disc is also double-sided, the trail of pits and lands extends to side two. DVD was originally said to stand for digital video disc, and later for digital versatile disc. Variations of the term DVD often describe the way data is stored on the discs: DVD-ROM has data which can only be read and not written, DVD-R and DVD+R can only record data once and then function as a DVD-ROM. DVD-RW, DVD+RW and DVD-RAM can both record and erase data multiple times.

Figure: DVD

The DVD specification supports disks with capacities from 4.7GB to 17GB and access rates of 600KBps to 1.3 MBps. One of the best features of DVD drives is that they are backward-compatible with CD-ROMs, meaning they can play old CD-ROMs, CD-I disks, and video CDs, as well as new DVD-ROMs. Newer DVD players can also read CD-R disks. Unlike CDs, DVDs can store an entire digitized motion picture. An additional benefit of DVD drives is that they are backward compatible with CD-ROMs, meaning that they can play CDs as well as DVDs. Backward compatible is an expression used to indicate that a new version of some technology still supports the specifications of the old version.

3. Blu-ray (BD) Discs

Blu-ray is an optical disc format designed to display high definition video and store large amounts of data. Blu-ray is the successor to DVD. Blu-ray makes use of the shorter wavelength of blue light to read and write even smaller pits on the optical disc surface for higher capacity. The standard was developed collaboratively by Hitachi, LG, Matsushita (Panasonic), Pioneer, Philips, Samsung, Sharp, Sony, and Thomson. The format's name comes from the fact that a blue laser reads from and writes to the disc rather than the red laser of DVD players.

A single-layer Blu-ray disc (25 GB) can hold a 135-minute high-definition movie and still have room for two hours of bonus material in standard definition. Two-layer discs storing 50 GB are available, and experiments with 20-layer discs have produced a 400 GB capacity. Blu-ray’s high capacity makes it the perfect media for distributing high-definition movies, which are too large to fit on a standard DVD.

Figure: Blu-ray Disc

Comparison of CD, DVD, and Blu-ray Disc with Varying Levels of Precision to Store

CDs, DVDs, and Blu-ray discs all use optical technologies with varying levels of precision to store increasing amounts of data in the same amount of space.

 Figure: CD, DVD, and Blu-ray

Magneto-Optical (MO) Drives

Magneto Optical (MO) drive is the latest of all storage devices. This drive uses both a laser and an electromagnet to record data on a removable cartridge. The surface of the cartridge contains tiny embedded magnets. Like magnetic disks, MO disks can be read and written to. And like floppy disks, they are also removable. The unique feature of MO drive is that it has a very high storage capacity, can be more than 200 MB, much greater than magnetic floppies. The MO drive is a popular way to back up files on a personal computer. Although MO drive is costlier and slower than Hard Disk Drive (HDD), it has a long life and is more reliable.

Figure: MO Disk

Advantages of Optical Disks

• The cost-per-bit of storage for optical disks is very low because of their low cost and enormous storage density.
• The use of a single spiral track makes optical disks an ideal storage medium for reading large blocks of sequential data, such as music.
• Optical disk drives do not have many mechanical read/write heads to rub against or crash into the dish surface. This makes optical disks a more reliable storage medium than magnetic tapes or magnetic disks.
• Optical disks have a data storage life in excess of 30 years. This makes them a better storage medium for data archiving as compared to magnetic tapes or magnetic disks.
• As data once stored on an optical disk becomes permanent, danger of stored data getting inadvertently erased/ overwritten is removed.
• Due to their compact size and light weight, optical disks are easy to handle, store, and port from one place to another.
• Music CDs can be played on a computer having a CD-ROM drive along with a sound board and speakers. This allows computer systems to be also used as music systems.

Limitations of Optical Disks

• It is largely read-only (permanent) storage medium. Data once recorded, cannot be erased and hence the optical disks cannot be reused.
• The data access speed for optical disks is slower than magnetic disks
• Optical disks require a complicated drive mechanism

Uses of Optical Disks

• For distributing large amounts of data at low cost
• For distribution of electronic version of conference proceeding, journals, magazines, books, product catalogs, etc.
• For distribution of new or upgraded versions of software products by software vendors

Input/ Output Device

Introduction

The input/ output devices provide the means of communication between the computer and the outer world. They are also known as peripheral devices because they surround the CPU and memory of a computer system. Input devices are used to enter data into primary storage and output devices accept results from the primary storage. The computer system consists of many input/ output devices to feed data into the computer and to see the result of processing done by the system.

Figure: Role of Input/ Output Devices

Users interact with computers through input/ output devices. Of all the computer hardware components, input/ output devices have the most direct impact on a user’s computing experience. To accommodate a wide variety of data and the many environments in which data is processed, there are literally hundreds of different input devices on the market. By learning about input devices, we also learn what computers are capable of. Output devices connect directly with our senses. Although most output from a computer is visual, much is auditory, and some exotic devices even affect our other senses. This section explores input and output and the different peripheral devices that users add to their computers to expand their functionality.

Input/ Output devices can be classified as either general purpose or special purpose. A general-purpose input/ output device is designed for use in a variety of environments. This category of I/O devices includes keyboards and displays. A special-purpose input/ output device is designed for one unique purpose. An example of a special-purpose input/ output device is the pill-sized camera from Given Imaging that, when swallowed, records images of the stomach and the small intestine as it passes through the digestive system. Another example of a special-purpose input device is the iPod’s patented Click Wheel that is used to navigate its menu system. The ability to “shake to shuffle” the song order on the iPod is also a form of input.

Input Device

An input device is any machine that feeds data into a computer. An input device may read the data in the form of text, numbers, image, audio or video, but the data given in any format will have to be converted into a machine readable format and this is done through input unit. This unit will transmit the data as a series of electrical pulses into the computer’s memory unit where it will be available for processing. The input device translates data into a code that can be read by the computer system’s electronic circuitry. Some input devices, such as the keyboard, enable the user to communicate directly with the machine. Others require data to be first recorded on an input medium such as paper or magnetized material.

Input devices can be classified into two types on the basis of direct involvement of computer:

1.      Offline- An operation that does not directly involve a computer.

2.      Online- An operation that directly involves a computer.

Offline Input Devices

Input devices that allow data entry operations without the direct involvement of a computer are called off-line input devices. Generally the input entered through this device is recorded on some media first and then processes by a computer later. For example key-to-punch, floppy disk etc. Most of lines are now obsolete and are very rarely used.

Online Input Devices

Online input devices provide direct and interactive communication between the user and the computer. The data from that device is sent directly to the computer with no need for intermediate media. These devices are economical when the volume of data is low and irregular. For example, Keyboard, Mouse, Punch cards, Light Pen, Joystick etc.  

Input devices can also be classified into the following two broad categories:

• Basic input devices

• Special input devices

The structure and function of common input devices of these two categories are discussed below in detail.

Basic Input Devices

The input devices which have now-a-days become essential to operate a PC (personal computer) may be called as “basic input devices.” These devices are always required for basic input operations. These devices include keyboard and mouse.

Special Input Devices

The input devices which are not essential to operate a PC are called as “special input devices.” These devices are used for various special purposes, and are generally not required for basic input operations. These devices include trackball, light pen, touch screen, joystick, digitizer, scanner, OMR, OCR, bar code reader, MICR and voice input devices.

Following are the commonly used input devices which are usually found to be present on most of the computer system in these days.

Keyboard and its use

Keyboard is an input device with various keys that enable you to enter alphanumeric data into a computer. It is similar to electronic typewriter keyboard but contain additional keys. It has been an effective device for inputting non-graphical data. Nowadays, a keyboard has also been provided with features to facilitate menu selection or graphical functions.

The standard layout of letters, numbers, and punctuation is known as a QWERTY keyboard because the first six keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters and was actually designed to slow typists down to avoid jamming the keys. Another keyboard design, which has letters positioned for speed typing is the DVORAK keyboard.  

Figure: Layout of Keys on QWERTY Keyboard

There are actually three different PC keyboards:

• Original PC keyboard with 83 keys.
• AT keyboard (Advanced technology keyboard) with 101 keys.
• Enhanced keyboard with 103 or 107 keys.

Computer keyboard has keys to perform specific tasks. The keys on computer keyboards are often classified as alphanumeric keys, punctuation keys, and special keys.

• Alphanumeric keys: letters and numbers
• Punctuation keys: comma, period, semicolon, and so on.
• Special keys: function keys, cursor control keys, modifier keys, caps lock, arrow keys etc.

Function keys (F1, F2, and so on) are usually arranged in a row along the top of the keyboard. They allow user to input commands without typing long strings of characters or navigating menus or dialog boxes. Most function key’s purpose depends on the program user is using. For example, in most programs, F1 is the help key. Most IBM-compatible keyboards have 12 function keys; most Macintosh systems have 15.

Cursor-movement keys let the user move around the screen. In many programs and operating systems, there is a mark on the screen where the characters we type will be entered. This mark, called the cursor or insertion point, can appear on the screen as a small box, a vertical line, or some other symbol that indicates our place in a document or command line.

Numeric keypad, usually located on the right side of the keyboard, looks like an adding machine, with its ten digits and mathematical operators (+, -, *, and /). It is used for fast entry and calculation of numeric data. The numeric keypad also features a Num Lock key, which forces the numeric keys to input numbers. When Num Lock key is deactivated, the numeric keypad’s keys perform cursor movement control and other functions.

In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Scroll Lock, Break, Caps Lock, Print Screen etc. Many companies have developed ergonomics keyboards, which reduce the strain while typing with the aim to prevent stress injuries. Microsoft’s natural keyboard is an example.  

 

Figure: A Typical Desktop Keyboard

How the Computer Accepts Input From the Keyboard

You might think the keyboard simply sends the letter of a pressed key to the computer- after all, that is what appears to happen. Actually, the process is more complex than that, as shown in the following figure.

Figure: How Input is received from the Keyboard.

A tiny computer chip, called the keyboard controller, notes that a key has been pressed. The keyboard controller places a code into part of its memory, called the keyboard buffer, indicating which key was pressed. (A buffer is a temporary storage area that holds data until it can be processed.) This code is called the key's scan code. The keyboard controller then signals the computer's system software that something has happened at the keyboard. It does not specify what has occurred, just that something has.

The signal the keyboard sends to the computer is a special kind of message called an interrupt request. (An interrupt is a signal; it notifies a program that an event has occurred.) The keyboard controller sends an interrupt request to the system software when it receives a complete keystroke. For example, if you type the letter s; the controller immediately issues an interrupt request. If you hold down the Shift key before typing the letter S, the controller waits until the whole key combination has been entered.

When the system software receives an interrupt request, it evaluates the request to determine the appropriate response. When a keypress has occurred, the system reads the memory location in the keyboard buffer that contains the scan code of the key that was pressed. It then passes the key's scan code to the CPU.

The keyboard buffer can store many keystrokes at one time. This capability is necessary because some time elapses between the pressing of a key and the computer's reading of that key from the keyboard buffer. With the keystrokes stored in a buffer, the program can react to them when it is convenient.

In many newer systems, the keyboard controller handles input from the computer's mouse and stores settings for both the keyboard and the mouse. One keyboard setting, repeat rate, determines how long you must hold down an alphanumeric key before the keyboard will repeat the character and how rapidly the character is retyped as long as you press the key. You can set the repeat rate to suit your typing abilities.

Mouse and its use

Mouse is a device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object you can roll along a hard, flat surface (usually on a desk or keyboard tray) and controls the pointer. The pointer is an on-screen object, usually an arrow, that is used to select text; access menus; and interact with programs, files, or data that appear on the screen. The mouse name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse's tail, and the fact that one must make it scurry along a surface. As you move the mouse, the pointer on the display screen moves in the same direction. Mice contain at least one button and sometimes as many as three, which have different functions depending on what program is running.

Figure: Mouse

Invented by Douglas Engelbart of Stanford Research Center in 1963, and pioneered by Xerox in the 1970s, the mouse is one of the great breakthroughs in computer ergonomics because it frees the user to a large extent from using the keyboard. In particular, the mouse is important for graphical user interfaces because you can simply point to options and objects and click a mouse button. Such applications are often called point-and-click programs. Using mouse involves five techniques- pointing, clicking, double-clicking, dragging and right clicking. The mouse is also useful for graphics programs that allow you to draw pictures by using the mouse like a pen, pencil, or paintbrush.

The advantages of the mouse are so numerous that it changed the entire personal computing industry. Although the Macintosh operating system was the first widely available system to take advantage of the mouse, the tool's popularity grew rapidly. By the late 1980s, IBM-compatible PCs were quickly adopting the mouse as a secondary input device.

Instead of forcing you to type or issue commands from the keyboard, the mouse and mouse-based operating systems let you choose commands from easy-to-use menus and dialog boxes. The result is a much more intuitive way to use computers. Instead of remembering obscure command names, users can figure out (sometimes pretty easily) where commands and options are located.

A mouse also allows you to create graphics such as lines, curves, and freehand shapes, on the screen. With this new capability, the mouse helped establish the computer as a versatile tool for graphic designers, starting what has since become a revolution in the graphic design field.

Types of Mice

There are three basic types of mice.

1.      Mechanical Mouse

2.      Opto-mechanical Mouse

3.      Optical Mouse

1. Mechanical Mouse

Mechanical has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.

2. Opto-mechanical Mouse

Opto-mechanical is same as a mechanical mouse but uses optical sensors (LEDs) to detect motion of the ball. There is horizontal and vertical roller inside the mouse. That roller helps to roll the mouse and calculate the coordinate points on the screen.

3. Optical Mouse

Optical mouse uses a laser to detect the mouse's movement. You must move the mouse along a special mat with a grid so that the optical mechanism has a frame of reference. Optical mice have no mechanical moving parts. They respond more quickly and precisely than mechanical and opto-mechanical mice, but they are also more expensive.

Connections

Mice connect to PCs in one of three ways:

·         Serial mice connect directly to an RS-232C serial port or a PS/2 port. This is the simplest type of connection.

·         Bus mice connect to the bus through an interface card. This is somewhat more complicated because you need to configure and install an expansion board.

·         Cordless mice aren't physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer.

The choice between the first two connections depends on whether you have a free serial port. If you do, it is usually simpler to connect a serial mouse. Cordless mice are more expensive than both serial and bus mice, but they do eliminate the cord, which can sometimes get in the way. Mice connect to Macintosh computers through the ADB (Apple Desktop bus) port.

Mousepad

Mousepad is a pad over which you can move a mouse. Mousepads provide more traction than smooth surfaces such as glass and wood, so they make it easier to move a mouse accurately. For mechanical mice, mousepads are optional. Optical mice, however, require special mousepads that have grids drawn on them.

Using the Mouse

You use a mouse to point to a location on the screen. Push the mouse forward across your desk, and the pointer moves up; push the mouse to the left, and the pointer moves to the left. To point to an object or location on the screen, you simply use the mouse to place the pointer on top of the object or location.

Everything you do with a mouse you accomplish by combining pointing with four other techniques: clicking, double-clicking, dragging, and right-clicking. Clicking, double-clicking, and dragging are illustrated in the following figure.

				“Click Click”                       Double- Click

 

Figure: Three Mouse Techniques

Clicking something with the mouse means to move the pointer to the item on the screen and to press and release the mouse button once. Double-clicking an item means to point to it with the mouse pointer and then press and release the mouse button twice in rapid succession. Dragging an item means to position the mouse pointer over the item, press the mouse button, and hold it down as you move the mouse. As you move the pointer, the item is "dragged" along with it. You can then drop the item in a new position on the screen. This technique is called drag-and-drop editing.

With Macintosh computers, most mice have only one button. With IBM-compatible computers, most mice have two buttons, but clicking, double-clicking, and dragging are usually carried out with the left mouse button. (In multibutton mice, one button must be designated as the "primary" button, referred to as the mouse button.) Some mice can have three or more buttons. The buttons' uses are determined by the computer's operating system, application software, and mouse-control software.

A fairly recent enhancement is the wheel mouse. A wheel mouse has a small wheel nestled among its buttons. You can use the wheel for various purposes, one of which is scrolling through long documents.

Microphone

Today, new computers have features that enable them to record audio and video input and play it back. Now that sound capabilities are standard in computer, microphones are becoming increasingly important as input devices to record speech. Spoken input is used most often in multimedia, where the presentation can benefit from narration. Most PCs now have phone-dialing capabilities, so if we have a microphone and speakers (or a headset microphone with an earphone), we can use your PC to make telephone calls.

Microphones also make the PC useful for audio conferencing over the Internet. For this type of sound input, we need a microphone and a sound card that translates the analog signal (that is, sound waves) from the microphone into digital codes the computer can store and process. This process is called digitizing. Sound cards can also translate digital sounds back into analog signals that can then be sent to the speakers.

Using simple audio recording software built into your Windows or Macintosh operating system, we can use a microphone to record our voice, thus creating files on disk. We can embed these files in documents, use them in Web pages, or e-mail them to other people.

There is also a demand for translating spoken words into text, much as there is a demand for translating handwriting into text. Translating voice to text is a capability known as speech recognition (or voice recognition). With it, you can dictate to the computer instead of typing, and you can control the computer with simple commands, such as "Open" or "Cancel." Speech-recognition programs usually require the use of a noise-canceling microphone (a microphone that filters out background noise).

Figure: Microphone

 Uses of Speech Recognition Systems

• For inputting data to a computer system by a person in situations where his/her hands are busy, or his/her eyes must be fixed on a measuring instrument or some other object
• For data input by dictation of long text or passage for later editing and review
• For authentication of a user by a computer system based on voice input
• For limited use of computers by individuals with physical disabilities

Track Ball

A trackball is a pointing device that works like an upside-down mouse. We use our thumb to move the exposed ball and our fingers to press the buttons.  The function of trackball is same as that of mouse but instead of moving a whole body of mouse, we can rotate ball and the body is fixed. The advantage of trackball over mice is that it is stationary so it does not require much space to use it. In addition, we can place a trackball on any type of surface, including our lap. Trackballs gained popularity with the advent of laptops, which typically are used on laps or on small work surfaces without room for a mouse.

Figure: Trackballs come in many different shapes and sizes

Like mice, trackballs come in different models. Some trackballs are large and heavy, with a ball about the same size as a cue ball. Others are much smaller. On portable computers, trackballs may be built directly into the keyboard, slide out of the system unit in a small drawer, or clamp to the side of the keyboard. Most trackballs feature two buttons, although three-button models are also available.

The Trackpad

The trackpad (also called a touchpad) is a stationary pointing device that many people find less tiring to use than a mouse or trackball. The movement of a finger across a small touch surface is translated into pointer movement on the computer screen. The touch-sensitive surface may be only 1.5 or 2 inches square, so the finger never has to move far. The trackpad's size also makes it suitable for a notebook computer. Some notebook models feature a built-in trackpad rather than a mouse or trackball (see Figure 3.13).

Figure: Notebook Computers with built-in Trackpad

Like mice, trackpads usually are separate from the keyboard in desktop computers and attach to the computer through a cord. Some special keyboards feature built-in trackpads. This feature keeps the pad handy and frees a port that would otherwise be used by the trackpad.

Trackpads include two or three buttons that perform the same functions as mouse buttons. Some trackpads are also "strike sensitive," meaning you can tap the pad with your fingertip instead of using the buttons.

One drawback of trackpads is that they must be kept clean and static-free. Buildup of dust and oils from the user's fingers can affect a trackpad's performance, making it less sensitive to the touch. An unwanted static charge can make a trackpad behave erratically.

Pointers in the Keyboard

Several computer manufacturers now offer another space-saving pointing device, consisting of a small joystick positioned near the middle of the keyboard, typically between the G and H keys. The joystick is controlled with either forefinger. Because users do not have to take their hands off the keyboard to use this device, it can save a great deal of time and effort. Two buttons that perform the same function as mouse buttons are just beneath the spacebar and are pressed with the thumb. Because it occupies so little space, the device is built into many different laptop models. This type of pointing device is also available on some models of desktop computer keyboards.

Several generic terms have emerged for this device; many manufacturers refer to it as an integrated pointing device, while others call it a 3-D point stick. On the IBM ThinkPad line of notebook computers, the pointing device is called the TrackPoint.

 

Figure: ThinkPad with the TrackPoint pointing device

Joystick

A joystick has a small vertical lever (called the stick) that moves in all directions and controls the movement of cursor. Most joysticks have buttons on top which is used to select the options. A joystick is similar to the mouse, except that with the mouse the cursor stops moving as soon as you stop moving the mouse. But with the joystick, the cursor continues moving in the direction joystick is pointing. To stop the cursor, you must return the joystick to its upright position. Most joysticks include two buttons which are called triggers. Joystick is often used for playing computer games, flight simulators, training simulators, and for controlling industrial robots.

Figure: Joystick

Digitizers

This is an input device that enables you to enter drawings and sketches into a computer. It converts/ digitizes pictures, maps and drawings into digital form for storage in computers. A digitizer consists of an electronic tablet and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons.

A pen (also called a stylus), which looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronics that enable it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer.

For digitizers, each point on the table represents a point on the display screen in a fixed manner. This differs from mice, in which at movement is relative to the current cursor position.

The static nature of digitizers makes them particularly effective for tracing drawings. Most modern digitizers also support a mouse emulation mode, in which the pen or cursor acts like a mouse.

Digitizers are also called digitizing tablets, graphics tablets, touch tablets, or simply tablets. It is commonly used in the area of Computer Aided Design (CAD) by architects and engineers to design cars, buildings, medical devices, robots, mechanical parts, etc. It is also used in the area of Geographical Information System (GIS) for digitizing maps available in paper form.

Figure: Digitizer

Light Pen

Light pen is a pointing device having the size and shape similar to that of a regular pen. It is used to select a displayed menu item or draw pictures on the monitor screen. The pen consists of a photocell and an optical system placed in a small tube. When its tip is moved over monitor and pen button is pressed, its photocell-sensing element detects the screen location and sends corresponding signal to CPU. Thus to identify a specific location, the light pen is very useful. But the light pen provides no information when held over a blank part of the screen because it is a passive device with a sensor only. The light pen is primarily used for graphics work. A typical use of light pen is in drawing lines of various thicknesses.

Figure: Light Pen

Scanner

Scanner is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use.  In other words a scanner copies an image, creates and stores it on a computer disk in a form that can be used by the computer. A scanner works by digitizing an image - dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen, and manipulated by programs. It consists of two components, the first one to illuminate the page so that the optical image can be captured and the other to convert the optical image into digital format for storage by computer.

Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR) system to translate the image into ASCII characters. More optical scanners sold today come with OCR packages.

Types of Scanners

The different types of scanners are:

1.      Flatbed scanners

2.      Portable scanners

3.      Integrated scanners

Flatbed scanners are designed to scan flat objects one page at a time, and they are the most common type of scanner. Flatbed scanners work in much the same way that photocopiers do—whatever is being scanned remains stationary while the scanning mechanism moves underneath it to capture the image. Some scanners can scan slides and film negatives, in addition to printed documents. Scanners designed for high-volume business processing come with automatic document feeders so that large quantities of paper documents can be scanned (one page after the other) with a single command.

Portable scanners are designed to capture text and other data while on the go. Some are full-page portable scanners that can capture images of an entire document (such as a printed document or receipt) encountered while on the go; others are handheld scanners designed to capture text one line at a time. In either case, the scanner is typically powered by batteries, the scanned content is stored in the scanner, and the content is transferred to a computer (via a cable or a wireless connection) when needed. Some handheld scanners can also be used to translate scanned text from one language to another.

Multimedia, medical, and some business applications may require the use of a three dimensional (3D) scanner, which can scan an item or person in 3D. Task-specific scanners, such as receipt scanners and business card scanners, are also available. In addition, scanning hardware is being incorporated into a growing number of products, such as ATM machines to scan the images of checks deposited into the machine; typically, the check images are printed on the deposit receipt and can be viewed online via online banking services

Flatbed Scanners Used to input photos, sketches, slides, book pages, and other relatively flat documents into the computer.	Portable Scanners Used to capture small amounts of text; the text is typically transferred to a computer at a later time.	Integrated Scanners Built into other devices, such as into the ATM machine shown here to capture images of deposited checks.

Figure: Different Types of Scanners

Scanners differ from one another in the following respects:

1. Scanning technology

Most scanners use charge-coupled device (CCD) arrays, which consist of tightly packed rows of light receptors that can detect variations in light intensity and frequency. The quality of the CCD array is probably the single most important factor affecting the quality of the scanner. Industry-strength drum scanners use a different technology that relies on a photomultiplier tube (PMT), but this type of scanner is much more expensive than the more common CCD -based scanners.

2. Resolution

The denser the bit map, the higher the resolution. Typically, scanners support resolutions from 72 to 600 dots per inch (dpi).

3. Sit depth

The number of bits used to represent each pixel. The greater the bit depth, the more colors or grayscales can be represented. For example, a 24-bit color scanner can represent 2 to the 24th power (16.7 million) colors. Note, however, that a large color range is useless if the CCD arrays are capable of detecting only a small number of distinct colors.

4. Size and shape

Hand-held scanners are adequate for small pictures and photos, but they are difficult to use if you need to scan an entire page of text or graphics. Larger scanners include machines into which you can feed sheets of paper. These are called sheet-fed scanners. Sheet-fed scanners are excellent for loose sheets of paper, but they are unable to handle bound documents. A second type of large scanner, called a flatbed scanner, is like a photocopy machine. It consists of a board on which you lay books, magazines, and other documents that you want to scan.

Magnetic ink character recognition (MICR)

MICR allows the computer to recognize characters printed using magnetic ink. MICR devices were developed to help the banking field in processing large volumes of cheques and deposits everyday. For that purpose magnetic ink is used to write character on the cheques and deposit forms, which are to be processed by an MICR. The MICR reads the character and compared with magnetized patterns stored in memory, thus identify them.

The cheque which can be processed by using MICR devices consists of bank’s identification code (name, branch, etc.) and customer’s account number being written using special ink that contains magnetized particles of iron oxide. As the cheques entered the reading unit, they pass through a magnetic field, which causes the particles in the ink to become magnetized. MICR reader-sorter reads these characters on cheques and sorts them for distribution to other banks or for further processing. It can read the documents with high degree of accuracy, even if the cheque are folded and roughly handled. Upto 3000 cheques are processed per minute by MICR. Main limitation of MICR device is that only 10 digits(0-9) and 4 special characters are used. MICR is not adopted by other industries because it supports only 14 symbols.

Figure: MICR Character Set (E13B Font)

Optical Character Recognition (OCR)

Optical character recognition refers to the branch of computer science that involves reading text from paper and translating the images into a form that the computer can manipulate (for example, into ASCII codes). An OCR system enables you to take a book or a magazine article and feed it directly into an electronic computer file.

All OCR systems include an optical scanner for reading text, and sophisticated software for analyzing images. OCR device examine each characters by analyzing the pixels of characters. When the whole characters are scanned, it is compared with standard characters in specific font in which the OCR devices are programmed to recognize the special characters. Most OCR systems use a combination of hardware (specialized circuit boards) and software to recognize characters, although some inexpensive systems do it entirely through software. Advanced OCR systems can read text in a large variety of fonts, but they still have difficulty with handwritten text.

OCR software is extremely complex because it is difficult to make a computer recognize an unlimited number of typefaces and fonts. Two standard OCR fonts are OCR-A (American standard) and OCR-B (European standard).

Optical Mark Recognition (OMR)

Optical Mark Recognition also called mark sensing, is a technology where an OMR device senses the presence or absence of a mark, such as a pencil mark. OMR device senses the marks by altering the intensity of light incident on the document and then sensing the reflected light received from the surface of the document. Intensity of reflected light received by a light sensor is less than that of the incident light due to the absorption by darker areas. Thus presence of a mark is registered by the intensity of reflected light received. OMR is very useful for grading tests with objective type questions, or for any input data that is of a choice or selection nature.

Optical Bar Recognition (OBR)

Optical Bar Recognition is a technology where an OBR device called bar code reader reads the bar coded data (data in the form of light and dark lines). The bar coded data consists of a number of bars of varying thickness and spacing between them. The bar code reader reads the bar coded data and converts it into electrical pulses which are then processed by computer. Bar coded data is generally used in labelling goods, numbering the books, or encoding ID or account numbers.

Universal Product Code (UPC) is the most widely known bar coding system. It uses standard code, which has vertical bars of varying widths- representing 10 digits. The first five digits represent the manufacturer and the second five digits identify the products.

Figure: An Example of UPC Bar Code

Touch Screen

Touch screen allows the user to touch the screen with his or her finger to select commands or otherwise provide input to the computer associated with the touch screen. Instead of using a pointing device such as a mouse or light pen, the user can use their finger to point directly to objects on the screen. Their use is becoming common with devices such as personal computers, mobile phones, mobile devices, and consumer kiosks in order to provide easy input.

Touch screens are appropriate in environments where dirt or weather would render keyboards and pointing devices useless, and where a simple, intuitive interface is important. They are well suited for simple applications such as automated teller machines or public information kiosks. Touch screens have become common in banking industry, fast food restaurants, department stores, drug stores, and supermarkets, where they are used for all kinds of purposes, from creating personalized greeting cards to selling lottery tickets.

Desktop Computers	Mobile Devices
Surface Computing Devices	Consumer Kiosks

Figure: Touch Screens

Digital Camera

Many people are switching from film to digits as they discover the convenience of digital photography. A digital camera captures images through the camera’s lens and stores them digitally rather than on film. The quality of a digital camera is typically judged on how many megapixels (millions of pixels) can be captured in an image. A pixel is one of many tiny dots that make up a picture in the computer’s memory. A traditional inexpensive film based camera produces 1.2-megapixel images. Today, most cell phones come with a 1.2- to 3-megapixel camera. We can buy a 10-megapixel digital camera for under Rs. 10,000. As with most technology, prices in the digital camera market are rapidly dropping. Most cameras capture images on a flash memory card that we can download to our PC using a USB cable or a wireless connection. Some computers and printers have flash memory card readers that allow us to download pictures directly to our PC or printer.

Figure: Digital Camera

Many digital cameras, in addition to taking still images, allow us to capture short video recordings. If we are interested in longer video, we can purchase a camcorder. A bit more costly, digital camcorders allow us to take full-length digital video that we can watch on our TV, download to our computer, or transfer to CD, DVD, or VCR tape. Many camcorders record direct to DVD, while others have high-definition capabilities. Webcams provide a lower-priced video camera for use as a computer input device. They are ideal for video conferencing over the Web.

Biometric Readers

Biometrics is the science of identifying individuals based on measurable biological characteristics. Biometric readers are used to read biometric data about a person so that the individual’s identity can be verified based on a particular unique physiological characteristic (such as a fingerprint or a face) or personal trait (such as a voice or a signature). As shown in the figure, a biometric reader can be stand-alone or built into another piece of hardware, such as a keyboard, a portable computer, an external hard drive, or a USB flash drive. Biometric readers can be used to allow only authorized users access to a computer or facility or to the data stored on a storage device, as well as to authorize electronic payments, log on to secure Web sites, or punch in and out of work.

STAND-ALONE FINGERPRINT READERS Often used to control access to facilities or computer systems, such as to the notebook computer shown here.	BUILT-IN FINGERPRINT READERS Typically used to control access to the device into which the reader is built, such as to the external hard drive shown here.

Figure: Biometric Readers

Output Device

Output is the process of translating data in machine-readable form into a form understandable by humans or readable by other machines. In simple words, output is a result of processing. Output can be meaningful information or gibberish (confused or meaningless), and it can appear in variety of forms- binary numbers, characters, pictures and as printed pages.

Output Device is a peripheral device that receives information from the CPU and present in to the user in the desired form. When a program is executed and the results computed, those results must be made available in a human readable form. The computer system needs an output device to communicate the processed information to the user. The output device translates processed data from a machine-coded form to a form that can be read and used by people.

The most common types of output devices are the monitor, which resembles a television screen, and the printer, which prints copy from the computer onto paper, magnetic tape, magnetic disk and floppy diskette. Another common output device is the graphics plotter, which produces graphics, charts or technical drawings on paper. A new type of output device being developed now is the speech synthesizer, a mechanism attached to the computer that produces verbal output sounding almost like human speech.

The output normally can be produced in two ways- either on a display unit/ device or on a paper. The various types of output devices on the basis of the kind of output they produce.

a) Softcopy devices

b) Hardcopy devices

Softcopy devices

A soft-copy output is a output, which is not printed on paper or on some materials. Softcopy output cannot be touched and cannot be carried for being shown to others. It is temporary in nature and vanishes after use. For example output displayed on a terminal screen or spoken out by a voice response system is a soft copy output.

Softcopy devices give screen displayed output which is lost when the computer is turned off. Softcopy devices enable viewing of work, which allow correction and rearrangement of materials to suit specific needs. Monitor, PC, projectors and VDT (Video Display Terminals) are the example of softcopy devices. They offer the following advantages:

ü  No expenditure on stationary

ü  Output can be seen faster

Hardcopy devices

A hard-copy output is a output, which is printed on paper or on some other materials. It can be touched and carried for being shown to others. They are permanent in nature and can be kept in paper files or can be looked at a later time when the person is not using the computer.

Printers, plotters are the examples of hardcopy output devices because they print the output in hard paper. The output is permanent in nature and cannot be changed.

Different types of output devices are used these days on the computer system. The major output devices are given below:

Visual Display Unit (VDU)/ Monitors

All computers are connected to some type of graphic display unit, which is called a monitor. It is the most popular soft-copy output device, which is used to display the information. Monitor is another term for display screen. However, the term monitor usually refers to the entire box, where as the display screen means just the screen. Monitors are available in many different types and size. The on-screen display enables us to see how applications are processing our data, but visual display unit is important to remember that the screen display is not permanent record i.e. the outputs are lost where the power is off.

Three basic type of monitor used are cathode ray tube (CRT), Liquid Crystal Display (LCD) and Plasma Display. CRT monitors look like a television and are used with non-portable computer systems. The thinner monitors used on notebook and other small computer are known as flat-panel displays. Compared to CRT (Cathode Ray Tube) based monitors, flat panel displays consume less electricity and take up much less room. Most flat panel displays use Liquid Crystal Display (LCD) technology. LCD displays sandwich cells containing tiny crystals between two transparent surfaces. By varying the electrical current supplied to each crystal, an images forms.

Classification of Monitors based on Color

There are many ways to classify monitors. The most basic is in terms of color capabilities, which separates monitors into three classes:

1. Monochrome monitors

Monochrome monitors display two colors, one for background and one for foreground. The colors can be black and white, green and black, or amber (yellowish-brown) and black. These monitors are used for text-only displays where the user does not need to see color graphics.

2. Gray-scale monitors

Gray-scale monitors are a special type of monochrome monitor capable of displaying different shades of gray (from a very light gray to black) against a white or off-white background, and are essentially a type of monochrome monitor. They are used in low-end portable systems (especially handheld computers) to keep costs down. Gray scale monitors are often classified by the numbers of bits they used to represent each pixel. For e.g., a 8 bit monitor represents each pixel with 8 bits. The more bits per pixel, more shades of gray the monitor can display.

3. Color monitors

Color monitors can display anywhere from 16 to over 16 million different colors. They are often called RGB monitor because they accept three different separate signals – red, green, blue. This differs from colour televisions, for example, which use composite video signals, in which all the colours are mixed together. All colour computer monitors are RGB monitors. An RGB monitor consists of a vacuum tube with three electron guns - one each for red, green, and blue at one end and the screen at the other end. The three electron guns fire electrons at the screen, which contains a phosphorous coating. When the electron beams excite the phosphors, they glow. Depending on which beam excites them, they glow red, green, or blue. Ideally, the three beams should converge for each point on the screen so that each pixel is a combination of the three colours.

Color monitors are often classified by the number of bits they use to represent each pixel. For example, a 24-bit monitor represents each pixel with 24 bits. The more bits per pixel, the more colors the monitor can display.

Classification of Monitors based on Signals

Another common way of classifying monitors is in terms of the type of signal they accept: analog or digital.

1. Digital Monitor

A digital monitor accepts digital signals rather than analog signals. All monitors (except flat-panel displays) use CRT technology, which is essentially analog. The term digital, therefore, refers only to the type of input received from the video adapter. A digital monitor then translates the digital signals into analog signals that control the actual display.

Although digital monitors are fast and produce clear images, they cannot display variable colors continuously. Consequently, only low-quality video standards, such as MDA (Monochrome Display Adapter), CGA (Colour Graphics Adapter), and EGA (Enhanced Graphics Adapter), specify digital signals. VGA (Video Graphics Array) and SVGA (Super VGA), on the other hand, require an analog monitor. Some monitors are capable of accepting either analog or digital signals.

2. Analog Monitor

This is the traditional type of color display screen that has been used for years in televisions. In reality, all monitors based on CRT technology (that is, all monitors except flat-panel displays) are analog. Some monitors, however, are called digital monitors because they accept digital signals from the video adapter. EGA monitors, for example, must be digital because the EGA standard specifies digital signals. Digital monitors must nevertheless translate the signals into an analog form before displaying images. Some monitors can accept both digital and analog signals.

Low-cost digital monitors are often called TIL (Transistor-Transistor Logic) monitors. Most monitors accept analog signals, which are required by the VGA, SVGA, 8514/A, and other high-resolution color standards. Some monitors are capable of accepting either type of signal.

Some monitors have fixed frequency, which means that they accept input at only one frequency. Another type of monitor, called a multi-scanning monitor, automatically adjusts to the frequency of the signals being sent to it. This means that it can accept input from different types of video adapters. Like fixed-frequency monitors, multi-scanning monitors accept TTL, analog, or both types of input.

Classification of Monitors based on Resolution

Depending upon the resolution, monitors can be classified as follows:

(a) CGA (Color Graphics Adapter)

(b) MDA (Monochrome Display Adapter)

(c) HGA (Hercules Graphics Adapter)

(d) EGA (Enhanced Graphics Adapter)

(e) VGA (Video Graphics Adapter)

(f) SVGA (Super VGA)

The differences between these monitors are summarized below:

Comparison among Different Types of Monitors
Type of Monitor	Display Type	Text Resolution	Graphics Resolution
CGA	Text and Graphics	Fair quality	320 x 200
MDA	Text only	Good quality	-
HGA	Text and Mono Graphics	Fair quality	320 x 200
EGA	Text and Enhanced Graphics	Good quality	640 x 350
VGA	Text and Video Graphics	Much better than all the above	640 x 480
SVGA	Text and Video Graphics	Text and Video Graphics	1600 x 1280

Factors Affecting Monitor Quality

Quality of monitor is often judged in terms of following factors:

• Monitor size
• Resolution
• Dot pitch
• Refresh rate
• Bandwidth
• Interlaced or Non-interlaced
• Convergence

Monitor size

The most important aspect of a monitor is its screen size. Like televisions, screen sizes are measured diagonally, in inches, the distance from lower left corner to the upper right corner diagonally. Typical monitors found in the market are of size 14 inches, and 17 inches and above. The size of display are determines monitor quality. In larger monitors, the objects look bigger or more objects can be fitted on the screen.

Resolution

The maximum number of points that can be displayed without overlap on a monitor screen is referred to as the resolution. The resolution of a monitor indicates how densely the pixels are packed. Pixel is short for Picture Element.  A pixel is a single point in a graphic image. Graphics monitors display pictures by dividing the display screen into thousands (or millions) of pixels, arranged in rows and columns. The pixels are so close together that they appear connected. The number of bits used to represent each pixel determines how many colours or shades of gray can be displayed. For example, an 8-bit colour monitor uses 8 bits for each pixel, making it possible to display 2 to the 8th power (256) different colours or shades of gray.

On color monitors, each pixel is actually composed of three dots – a Red, Green and Blue. Ideally, the three points should converge at the same point, but all monitors have some convergence error that can make colour pixels appear fuzzy.

Resolution indicates the quality of monitor. Greater the number of pixels, better the resolution and sharper the image. Actually the resolution is determined by the video controller or video adapter card, not by the monitor itself, most monitor specifications list a range of resolutions.

Dot pitch

Dot pitch is the distance between the phosphor dots that make up a single pixel on a display screen. Measured in millimeters, the dot pitch is one of the principal characteristics that determine the quality of display monitors. The smaller the dot pitch, the crisper the display image. The dot pitch of color monitors for personal computers ranges from about 0.15 mm to 0.28 mm. Another term for dot pitch is phosphor pitch.

Figure: Dot Pitch

Refresh Rate

Display monitors must be refreshed many times per second. The refresh rate is the number of times per second that the electron guns scan every pixel on the screen and is measured in Hertz (Hz), or in cycles per second.

The refresh rate is an important concern because phosphor dots fade quickly after the electron gun passes over them. Therefore, if the screen is not refreshed often enough, it appears to flicker, and flicker is one of the main causes of eyestrain. The problem is compounded because we may not even detect the flicker; in the long run, it can still cause eyestrain.

The old standard for monitor refresh rates was 60Hz, but a new standard developed by VESA sets the refresh rate at 75Hz for VGA and SVGA monitors. The faster the refresh rate, the less the monitor flickers.

Bandwidth

It is the amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits or bytes per second (bps). For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

Interlaced or Non-interlaced

Interlacing is a display technique that enables a monitor to provide more resolution inexpensively. With interlacing monitors, the electron guns draw only half the horizontal lines with each pass (for example, all odd lines on one pass and all even lines on the next pass). Because an interlacing monitor refreshes only half the lines at one time, it can display twice as many lines per refresh cycle, giving it greater resolution. Another way of looking at it is that interlacing provides the same resolution as non-interlacing, but less expensively. A shortcoming of interlacing is that the reaction time is slower, so programs that depend on quick refresh rates (animation and video, for example), may experience flickering or streaking. Given two monitors that offer the same resolution, the non-interlacing one will generally be better.

Convergence

Convergence refers to how sharply an individual colour pixel on a monitor appears. Each pixel is composed of three dots - a red, blue, and green. If the dots are badly misconverged, the pixel will appear blurry. All monitors have some convergence errors, but they differ in degree.

There are three categories of display screen technology. They are given below:

1. Cathode Ray Tube (CRT)

2. Liquid Crystal Display (LCD)

3. Plasma Display

CRT and its use

CRT monitors look like a television and are normally used with non-portable computer systems. CRT monitors use the same cathode-ray tube technology used in conventional televisions in which an electron gun sealed inside a large glass tube projects an electron beam at a screen coated with red, green, and blue phosphor dots; the beam lights up the appropriate colours in each pixel to display the necessary image. As a result, CRTs are large, bulky, and heavy.

Figure: How a CRT monitor creates an image

The above figure shows how a typical CRT monitor works. Near the back of a monochrome or gray-scale monitor housing is an electron gun. The gun shoots a beam of electrons through a magnetic coil, which aims the beam at the front of the monitor. The back of the monitor's screen is coated with phosphors, chemicals that glow when they are struck by the electron beam. The screen's phosphor coating is organized into a grid of dots. The smallest number of phosphor dots that the gun can focus on is called a pixel, a contraction of the term picture element. Modern monochrome and gray-scale monitors can focus on pixels as small as a single phosphor dot.

Actually, the electron gun does not just focus on a spot and shoot electrons at it. It systematically aims at every pixel on the screen, starting at the top left corner and scanning to the right edge. Then it drops down a tiny distance and scans another line until it reaches the bottom of the screen. Then it starts over. As the electron gun scans, the circuitry driving the monitor adjusts the intensity of each beam to determine whether a pixel is on or off or, in the case of gray-scale, how brightly each pixel glows.

A colour monitor works like a monochrome one, except that there are three electron beams instead of one. The three guns represent the primary additive colours (red, green, and blue), although the beams they emit are colourless. In a colour monitor, each pixel includes three phosphors- red, green, and blue- arranged in a triangle. When the beams of each of these guns are combined and focused on a pixel, the phosphors light up. The monitor can display different colours by combining various intensities of the three beams.

A CRT monitor contains a shadow mask, which is a fine mesh made of metal, fitted to the shape and size of the screen. The holes in the shadow mask's mesh are used to align the electron beams, to ensure that they strike precisely the correct phosphor dot. In most shadow masks, these holes are arranged in triangles.

Types of CRT monitors

There are two types of CRT monitors:

i. Composite CRT monitors

Composite CRT monitor uses only one electron gun to control the intensity of all these phosphorus dots in each pixel.

ii. RGB CRT monitors

RGB CRT monitor uses three individual guns, one for its dot, to control the intensity. Each of the sub dots are hit by its own electron gun that is why these monitors give sharper picture.

Advantages of CRT

a) CRT monitors have wider viewing angle.

b) CRT monitors are cheaper and durable.

c) CRT monitors give sharp and crisp images.

d) CRT monitors resolution is adjustable.

Disadvantage of CRT

a) As the phosphor dots start to fade after sometime they are hit by the electron gun, they need to be refreshed again.

b) The screen may flicker causing eyestrain.

c) They are bulky and heavy.

d) They consume high power.

LCD and its use

While CRT monitors are still in use, most computers today (as well as most television sets) use the thinner and lighter flat-panel displays. Flat-panel display technology is also used in the display screens integrated into mobile phones and consumer electronics. Flat-panel displays form images by manipulating electronically charged chemicals or gases sandwiched between thin panes of glass or other transparent material. Flat-panel displays take up less desk space, which makes it possible to use multiple monitors working together to increase the amount of data the user can view at one time, increasing productivity. Flat-panel displays also consume less power than CRTs and most use digital signals to display images (instead of the analog signals used with CRT monitors), which allows for sharper images.

There are several types of flat-panel monitors, but the most common is the liquid crystal display (LCD) monitor. The LCD monitor creates images with a special kind of liquid crystal that is normally transparent but becomes opaque when charged with electricity. When a voltage is applied, the crystals line up in a way that blocks light from passing through them and the absence of light is seen as characters on the screen. If we have a handheld calculator or a digital watch, it probably uses a liquid crystal display. The LCD screen is flat, since it does not have picture tube. Instead the screen image is generated on a flat plastic disk. Thus, LCD screens are much thinner, soft and don’t flicker as compared to CRT.

One disadvantage of LCD monitors is that, unlike phosphor, the liquid crystal does not emit light, so there is not enough contrast between the images and the background to make them legible under all conditions. The problem is solved by backlighting the screen. Although this makes the screen easier to read, it requires additional power. Another disadvantage of LCD monitors is their limited viewing angle - that is, the angle from which the display's image can be viewed clearly. With most CRT monitors, we can see the image clearly even when standing at an angle to the screen. In LCD monitors, however, the viewing angle shrinks; as we increase our angle to the screen, the image becomes fuzzy quickly. In many older flat-panel systems, the user must face the screen nearly straight on to see the image clearly. Technological improvements have extended the viewing angles of flat-panel monitors but have also caused their prices to increase.

There are two main categories of liquid crystal displays: active matrix and passive matrix. Passive matrix LCD relies on transistors for each row and each column of pixels, thus creating a grid that defines the location of each pixel. The colour displayed by a pixel is determined by the electricity coming from the transistors at the end of the row and the top of the column. The advantage of passive matrix monitors is that they are less expensive than active matrix, a major consideration in laptops where the monitor can account for one-third the cost of the entire computer. One disadvantage is that passive matrix LCD displays have a narrow viewing angle. Another disadvantage is that passive matrix displays do not "refresh" the pixels very often. If you move the pointer too quickly, it seems to disappear, an effect known as submarining. Also, animated graphics can appear blurry.

Most notebooks that use passive matrix technology now refer to their screens as dual-scan LCD. In dual-scan LCD, the problem of the refresh rate is lessened by scanning through the pixels twice as often. Thus, submarining and blurry graphics are less troublesome than they were before the dual-scan technique was developed.

Active matrix LCD technology assigns a transistor to each pixel, and each pixel is turned on and off individually. This enhancement allows the pixels to be refreshed much more rapidly, so submarining is not a problem with these monitors. In addition, active matrix screens have a wider viewing angle than dual-scan screens. Active matrix displays are often called thin-film transistor (TFT) displays because many active matrix monitors are based on TFT technology, which employs as many as four transistors per pixel. Active matrix displays are considerably more complex than passive matrix screens and are therefore considerably more expensive. The performance gains, however, are worth the cost for many users.

Advantages of LCD

1. LCD is light weight, flat, thin and requires less space.
2. LCD does not require periodic refreshing.
3. LCD emits zero radiation thereby avoiding eye strain.
4. LCD consumes less power.

Disadvantages of LCD

1. LCD have smaller viewing angle so picture is best viewed when the person is in straight position from the centre of monitor.
2. The liquid crystals do not emit light so the images are less sharp.
3. There is a need of backlight setting to enhance sharpness of images.
4. Resolution is normally set.

CRT comparison to LCD Monitors

Feature	CRT	LCD
Resolution	Fixed resolution is only optimal at published resolution.	Fixed pixel format will support resolutions lower or higher than native resolution
Refresh Rates	Only flicker-free if the refresh rate is 75Hz or higher.	Virtually flicker-free
Color	True color must be calibrated	True color temperatures can be simulated
Picture Formation	Because pixels are formed by grouping multiple dots or stripes, pictures are not as sharp.	Individually formed pixels provide excellent focus, clarity and sharpness. Pictures appear smoother
Viewing Angle	Excellent viewing angle.	Limited to 160 degrees.
Power	Emissions and electro-magnetic interferences are always present.	Use 70% less energy. No emissions.
Display Interface	Only remaining analog device among digital computers.	Digital, but most come with an analog interface for plug-n-play compatibility.
Brightness and Contrast	CRT monitors have a maximum brightness of only 150 nits.	Brightness levels are measured in nits. Active matrix LCD monitors range from 150 to 280 nits.
Price	Less expensive than LCD.	Costs three or four times more with similar viewing areas, resolutions and other features.

Plasma Display

A plasma display panel is a type of flat panel display used for large TV displays (typically above 37-inch or 940 mm). These thin displays are created by sandwiching a special gas (such as neon or xenon) between two sheets of glass. When the gas is electrified via a grid of small electrodes, it glows. By controlling the amount of voltage applied at various points on the grid, each point acts as a pixel to display an image. Plasma displays are expensive, but they provide high-quality images and can be much larger than typical LCDs. Some plasma displays are big enough to be hung on a wall and used like a large-screen television.

The use of plasma in displays became popular in the late 1990s because it could be used to create large, flat, thin televisions at a reasonable cost. Compared to conventional CRT displays, plasma displays are about one-tenth the thickness--around 4'', and one-sixth the weight--under 67 pounds for a 40" display. They use over 16 million colors and have a 160 degree-viewing angle. While they offer excellent picture quality, they are quite expensive and are fast becoming the popular choice for HDTV.

Advantages of Plasma Display

• High contrast. The best, compared to LCD and tube screens. The image is colourful and bright. That’s why plasma screens are often chosen for home theatre.
• Plasma screen is not as persistent as LCD screen; the response time is not long. So, the dynamic scenes will look natural.
• Plasma screens have larger viewing angle, compared to LCD screens. The image quality won’t change due to the position of watching.
• Compared to CRT screen, there is no image flicker, so your eyes won’t get tired.
• They are insensitive to electromagnetic fields. Magnetic materials are used in the production of speakers, so they can’t be placed near the CRT screen. Plasma screens don’t have this disadvantage.

Disadvantages of Plasma Display

• Very high price – about few thousand dollars.
• High energy consumption. For example, LCD screens of the same size consume few times less energy.
• As a result of high energy consumption, plasma screens get hot, that’s why producers use fans for cooling. It means that the fan will make noise. Of course, producers use fans with lowered noise level and besides, the viewer is quite far from the screen.
• Plasma screens have the same disadvantage as CRT TV-sets – their phosphor fades, especially on the places with stable images, for example, channel logos. It means, that it isn’t recommended to use them as a TV-set. Though the producers try to cope with this disadvantage and nowadays its term of life is compared to other screen types. Besides, the dots of plasma screen can also fade.
• As in any other screen type, the unit of image is a dot or a pixel. In plasma screen this dot is bigger than in other types. That’s why plasma screens are large (from 30 inches). It means that the room, where you are going to place the screen, should be quite big – the distance between the viewer and the screen should be 4-5 times bigger than its diagonal, i.e. 3-4 meters. Back speakers should be behind the viewer, so the width of the room should be minimum 4-5 meters.
• Plasma screens are heavy

LCD comparison to Plasma Display

Features	LCD	Plasma Display
Size	Commonly 13 to 52 inches. Larger sizes are available but very expensive.	Commonly 42 to 63 inches. More choice is available for 50 inch and above. Larger sizes are available but are very expensive.
Viewing Angle & Off Angle	Standard of 160, but up to 175 degrees (depends on model). Slight picture fading at extreme angles.	Up to 178 degrees (depends on model). Off-angle viewing is excellent and better than LCD.
Resolution, Brightness and More	Generally offers slightly higher resolution than Plasma. Not as good contrast ratio. Anti-glare makes it better for viewing in bright rooms. Newer technology offers improved black levels, but still not as good as plasma for producing blacks.	Higher levels of brightness and contrast.  Viewing quality best where lighting can be controlled. Better display of black.
Weight, Durability, Power Consumption	Lighter than Plasma. Also more durable than Plasma. Consumes 30 to 40 percent less power than plasma of similar size.	Very heavy and usually needs special wall-mount brackets. Plasma are more fragile and also consumes more power than LCD.
High Altitude Performance	Not affected by high altitude.	Anything above 6,500 feet can affect the performance.
Inherent Issues	LCD televisions may suffer from a defective pixel (also called a stuck pixel or dead pixel). This is a single pixel on the display that always remains lit or dark, usually the result of a transistor malfunction or uneven distribution of liquid in the LCD.	Plasma can suffer from "burn in" the term used to describe a ghosting of an image that can remain on the screen if a stationary image has been left on too long. Burn in has been reduced in newer models.
Lifespan 60,000 hours is equivalent to five years of 24/7 usage, or approximately 27 years of typical family TV use.	Typically you can expect 50-60,000 hours. With some LCDs you may be able to replace the the fluorescent lamps. Compare with older CRT televisions that typically had a lifespan of 25,000 hours	Many newer plasma displays also have reached a lifespan of 60,000 hours and higher. Plasma displays, however, will slowly lose some brightness over a long period of time. This brightness lose is called LTHB (Life to Half Brightness).
Price	Typically, you can expect LCD televisions in the 42-inch and below range to be a better-price when compared to plasma televisions below 42 inches.	Typically you can expect plasma televisions in the 42-inch and above range to be a better price when compared to LCD televisions above 42 inch.

Video Controller

The quality of the images that a monitor can display is defined as much by the video controller as by the monitor itself. The video controller is an intermediary device between the CPU and the monitor. It contains the video-dedicated memory and other circuitry necessary to send information to the monitor for display on the screen. It consists of a circuit board, usually referred to simply as a card (the terms video card and video controller have the same meaning), which is attached to the computer's motherboard. Within the monitor's constraints, the controller's processing power determines the refresh rate, resolution, and number of colors that can be displayed.

Figure: The video controller connects the CPU, via the data bus on the motherboard, to the monitor

The video controller contains its own on-board processor and memory, called video RAM (VRAM). VRAM is dual-ported, meaning that it can send a screen full of data to the monitor and at the same time receive the next screen full of data from the CPU. It is faster and more expensive than DRAM (dynamic RAM), the type of memory chip used as RAM for the CPU. Users with large monitors or with heavy graphics needs will usually require more than 4 MB of video RAM. Special video controllers-designed for use with large monitors or for fast, full-motion video-may have as much 32 MB of on-board RAM and support resolutions up to 1900 X 1200.

Data and Multimedia Projectors

A data projector is used to display output from a computer to a wall or projection screen. Conventional data projectors are often found in classrooms, conference rooms, and similar locations and can be freestanding units or permanently mounted onto the ceiling. While most data projectors connect via cable to a computer, wireless projectors that use a Wi-Fi connection are available. Some projectors also include an iPod dock to connect a video iPod in order to project videos stored on that device.

Another type of data projector is the integrated projector—tiny projectors that are beginning to be built into mobile phones, portable computers, portable digital media players, and other portable devices to enable the device to project an image (such as a document, presentation, or movie) onto a wall or other flat surface from up to 12 feet away. These integrated projectors typically create a display up to 10 feet wide in order to easily share information on the device with others on the go without having to crowd around a tiny screen. This same technology is also incorporated into very small stand-alone portable projectors that can be used for making presentations while on the go. Another type of data projector is designed to project actual 3D projections or holograms. For instance, holograms of individuals and objects can be projected onto a stage for a presentation and hologram display devices can be used in retail stores, exhibitions, and other locations to showcase products or other items in 3D.

CONVENTIONAL DATA  PROJECTORS Frequently used for both business and classroom presentations.	INTEGRATED AND PORTABLE PROJECTORS Images displayed on the device (such as the mobile phone shown here) are projected onto any surface.	HOLOGRAPHIC PROJECTORS Project 3D images of objects or individuals

Figure: Data Projectors

Printer

Printers are one of the most popular output devices available for personal computers. Printer is the hard-copy output device that prints text or any other information on paper and in many cases on transparencies and other media. Printers have been around since the early days of computer. The first printers were actually typewriters and teletypewriters that were adapted to print binary data. These printers were often slow and noisy. Today, these are printers that print entire pages of text and/or graphics at astonishing speeds.

Printer quality available from the hard copy output varies considerably.

1. Letter quality print: Letter quality print is made using fully formed characters and is obtained by striking with the hammer containing fully formed solid line characters and symbols.

2. Near-letter quality print: Near-letter quality print obtained from dots that arrange them to form alphanumeric characters. Print head makes multiple passes over the same letters filling in the space between dots or lines.

3. Standard quality print: Standard quality print quality is produced when characters composed of dots are formed by a single pass of print head.

4. Draft quality print: Draft quality print is the lowest quality print in which the characters are formed by using minimum number of dots. Draft quality print is suitable for rough draft.

Features Determining Printer Quality

While determining printer quality, following factors should be considered important.

1. Resolution: All printers work by laying down tiny dots of ink, toner or dye. The dots are so small and close together that they fool our eye into thinking its seeing solid images. The more dots per inch a printer can produce, the better is its image quality. This characteristic is known as “print resolution“. Resolution is measured in linear dots per inch, or “dpi”. Medium quality inkjet or laser printer can print 300 or 600 dip. The best quality printer can have the resolutions of 1200 to 1800 dip.

2. Speed: Printer speed is measured in either character per second (cps) or pages per minute (ppm). Most printers have different cps or ppm ratings for text and graphics because graphics usually take longer to print. Normal laser printer can have the speed of 4-24 ppm.

3. Duty cycle: Duty cycle, which is generally expressed in pages per month, refers to how hard you can work printer before it breaks. Heavy Duty cycle printers are required for offices having large volume of works.

Types of Printer

Printers are classified as impact or non- impact printers, depending on the method used to print the characters on the paper.

1. Impact Printer

An impact printer creates an image by pressing an inked ribbon against the paper, using pins or hammers to shape the image. A simple example of an impact printer is a typewriter, which uses small hammers to strike the ribbon. Each hammer is embossed with the shape of an alphanumeric character; that shape is transferred through the inked ribbon onto the paper, resulting in a printed character.

Many modern electric typewriters can be connected to a PC and used as a letter quality printer. As a printer, however, even a good typewriter is slow and limited in the kinds of images it can produce.

Impact printer makes a lot of noise while printing. They can produce multiple copies of a document at the same time. Impact printers are of two types according to their printing speed, they are character printers and line printers.

a. Character Printers

These printers print one character at a time. These printers are further of two types:

1. Daisy Wheel Printers
2. Dot Matrix Printers

Daisy Wheel Printers

These printers print the characters by a mechanism that uses a plastic or metal hub with spokes, called daisy wheel. The characters are embossed on the radiating spokes and printed by striking these spokes against the ribbon and paper. These printers give a good quality but cannot print graphics. They are noisy and slow, printing from 10 to about 75 characters per second. Also they more expensive than dot matrix printers.

Figure: Daisy Wheel Printer

Dot Matrix Printer

These printers print the characters and all kinds of images by putting dots onto paper. They print many special characters, different sizes of print and graphics such as charts and graphics. These printers can produce multiple sheets of documents very quickly in a single print by using carbon papers. They are also used to print very wide sheets, as data processing departments often use when generating large reports with wide columns of information. But they do not give better printing quality than daisy wheel printers. Compared to laser and ink-jet printers, dot matrix printers are notorious for making noise. The printing speed of a dot matrix printer can be upto 360 cps (characters per second). They are widely used with microcomputers in most of the offices. It is very useful for high- volume work (low quality) because of low printing cost.

Figure: Dot Matrix Printer

A dot matrix printer creates an image by using a mechanism called a print head, which contains a cluster (or matrix) of short pins arranged in one or more columns. On receiving instructions from the PC, the printer can push any of the pins out, in any combination. By pushing out pins in various combinations, the print head can create alphanumeric characters

Figure: How a dot matrix printer creates an image

When pushed out from the cluster, the protruding pins' ends strike a ribbon, which is held in place between the print head and the paper. When the pins strike the ribbon, they press ink from the ribbon onto a piece of paper. Where a single pin strikes the ribbon, a single dot of ink is printed on the page, hence the printer name, dot matrix. The more pins that a print head contains, the higher the printer's resolution. The lowest resolution dot matrix printers have only nine pins; the highest resolution printers have twenty-four pins.

Whereas other types of printers have their speed measured in pages per minute, dot matrix printers are measured in characters per second (cps). The slowest dot matrix printers create fifty to seventy characters per second; the fastest print more than 500 cps.

b. Line Printers

These printers print one line at a time. Their printing speed is much more than character printers. They are also of two types:

1. Drum Printers
2. Chain Printers

Drum Printers

These printers print line by a rotating drum having a ring of characters for each print position. The hammers strike each character of the drum simultaneously so that entire line is printed in one full rotation of the drum. These printers are also called as “barrel printers.” Thus a drum printer with 132 characters per line abs supporting a character set of 96 characters will have altogether 12,672 (132 x 96) characters embossed on its surface.

Figure: The printing mechanism of a Drum Printer

It also consists of hammers or print head, one for each character position in the line, are mounted in the front of the drum. The total number of hammers is equal to the total number of print positions. The paper to print is placed between the drum and the hammers. Drum printers are expensive. The user cannot change printer drums so they have fixed character set. The printouts obtained from these printers have even character spacing but uneven line height.

Chain Printers

A chain printer consists of a metallic chain on which all the characters of the character set supported by the printer are embossed. A standard character set may have 48, 64 or 96 characters. Rows of hammers/print heads are mounted in the front of the chain. The total number of hammers is equal to the total number of print positions. The chain rotates continuously on horizontal plane. The hammer corresponds to a position on the line strikes the paper when the specific character to be printed at that position comes below the hammer.

In chain printer to the character in the character set are embossed several times that enhance the quality of printing. An advantage of the chain printer is that chain can be easily changed, so different character set can be used. The printouts obtained from these printers have uneven character spacing but even line height.

Figure: The printing mechanism of a Chain Printer

2. Non-impact Printer

Non-impact printers do not make contact with paper or ribbon during printers printing. They use several technology for printing, such as xerographic, electrostatic, electro sensitive, electro thermal, ink jet, and laser. These printers print a complete page at a time and, therefore, are also called as “page printers.” Non impact printers are the fastest of printers with speeds approximation 20,000 lines of print per minute. They are also much quieter than impact printers.

In the early years of computing, dot matrix printers were the most commonly used printing devices. They are not as prevalent now, although dot matrix printers are still popular in business and academic settings because they are relatively fast and inexpensive to operate, and they do a good job of printing text and simple graphics. Because ink jet printers now offer much higher quality for about the same price, they have become more popular than dot matrix printers in homes and small businesses. Laser printers are also popular in homes and businesses, even though they are more expensive to buy and operate than either ink jet or dot matrix devices.

The various types of non-impact printers are explained below:

Ink Jet Printers

Ink jet printer prints character by spraying ink having high iron content at a sheet of paper. Magnetized plates in the ink’s path direct the ink into the paper in the desired shapes. Ink-jet printers are capable of producing high quality print approaching that produced by laser printers. A typical ink-jet printer provides a resolution of 300 dots per inch, although some newer model offers higher resolutions. Ink-jet printers are non-impact printers because they print by spraying ink on papers. These printers can print many special characters, different sizes of print, and graphics such as charts and graphs.

Some printers print with one single-sized ink droplet; others print using different-sized ink droplets and using multiple nozzles or varying electrical charges for more precise printing. The print head for an ink-jet printer typically travels back and forth across the page, which is one reason why ink-jet printers are slower than laser printers. However, an emerging type of ink-jet printer uses a printhead that is the full width of the paper, which allows the printhead to remain stationary while the paper feeds past it. These printers are very fast, printing up to 60 ppm for letter-sized paper.

In general, the price of ink-jet printers is lower than laser printers. Color ink-jet printers provide an inexpensive way to print full color documents. The draw backs of ink-jet printers are they are slower and they require a special type of ink that is suitable to mark on inexpensive paper.

   Figure: How Ink Jet Printer Works

Compared to laser printers, the operating cost of an ink jet printer is relatively low. Expensive maintenance is rare, and the only part that needs routine replacement is the ink cartridge. Many ink jet printers use one cartridge for color printing and a separate black-only cartridge for black-and-white printing. This feature saves money by reserving colored ink only for color printing.

Another improvement in ink jet printers has been in the paper they require. For many years, they needed a special paper, and each sheet had to dry before you could touch it. Today, you can run normal photocopy paper through most ink jet printers (although glossy paper looks slightly better), and the ink is dry within a few seconds.

Finally, ink jet printers offer a cost-effective way to print in color. Color ink jet printers have four ink nozzles: cyan (blue), magenta (red), yellow, and black. These four colors are used in almost all color printing because it is possible to combine them to create any color in the visible spectrum. Notice that the colors are different from the primary additive colors (red, green, and blue) used in monitors. Printed color is the result of light bouncing off the paper, not color transmitted directly from a light source. Consequently, cyan, magenta, yellow, and black are sometimes called subtractive colors and color printing is sometimes called four-color printing.

Laser Printer

Laser printer utilizes a laser beam to produce an image on a drum. Laser printers produce high-quality print and are capable of printing an almost unlimited variety of fonts. These printers look and work like photocopiers. They are based on laser technology which is the latest development in high speed and high quality printing.

Laser printers are the standard for business documents and come in both personal and network versions; they are also available as both color and black-and-white printers. To print a document, the laser printer first uses a laser beam to charge the appropriate locations on a drum to form the page’s image, and then toner powder (powdered ink) is released from a toner cartridge and sticks to the drum. The toner is then transferred to a piece of paper when the paper is rolled over the drum, and a heating unit fuses the toner powder to the paper to permanently form the image (see figure). Laser printers print one entire page at a time and are typically faster and have better quality output than ink-jet printers. Common print resolutions for laser printers are between 600 and 2,400 dpi; speeds for personal laser printers range from about 15 to 30 ppm.

Figure: How Laser Printer Works?

Laser printers are very popular and have become an essential part of Desk Top Publishing (DTP). Although laser printers are costlier than dot matrix, yet they are generally preferred in all offices due to their high quality of printing. Laser printers are non-impact printers, so they are much quieter than impact printers. They are relatively fast, although not as fast as some dot-matrix printers. The speed of laser printers ranges from about 10 to 200 pages of text per minute (ppm). Laser printer is expensive to buy and operation cost is also high. Note: 6ppm is equivalent to 40 characters per second.

Laser printers are controlled through page description languages (PDLs). There are two de facto standards for PDLs:

• PCL- Hewlett-Packard (HP) was one of the pioneers of laser printers and has developed a Printer Control Language (PCL) to control output. There are several versions of PCL, so a printer may be compatible with one but not another. In addition, many printers that claim compatibility cannot accept HP font cartridges.
• PostScript - This is the de facto standard for Apple Macintosh printers and for all desktop publishing systems.

Most software can print using either of these PDLs. PostScript tends to be a bit more expensive, but it has some features that PCL lacks and it is the standard for desktop publishing. Some printers support both PCL and PostScript.

Difference between Impact Printer and Non-impact Printer

Impact Printer	Non-impact Printer
Text or image is formed in contact of paper and the printer head.	Text or image is formed without any physical contact of the paper and the printer head.
Noisy, slow and poor quality output.	Noiseless, fast and high quality output.
These printers are cheaper. And also the operation costs is lesser.	These printers are expensive. And also the operation costs is more.
Can print only one specific font (except dot matrix printer)	Can print characters of almost all fonts
Can print only text, but cannot print graphics	Can print text as well as graphics
Print quality is comparatively low	Print quality is comparatively high.
Example – Dot matrix.	Example – Laser and Ink-jet.

Thermal Printer

Thermal printers are printers that produce images by pushing electrically heated pins against special heat-sensitive paper. These printers print characters by melting a wax-based ink off a ribbon onto a special heat sensitive paper. These printers are used primarily for presentations graphics and handouts. Thermal printers are inexpensive and are used in most calculators and many fax machines. They produce low- quality print, and the paper tends to curl and fade after a few weeks or months.

Snapshot Printer

With digital cameras and scanners becoming increasingly popular, users want to be able to print the images they create or scan. While the average color ink jet or laser printer can handle this job satisfactorily, many people are investing in special snapshot printers. These small-format printers use special glossy paper to create medium-resolution prints of 150 to 200 dpi. The best snapshot printers can create images that look nearly as good as a photograph printed using traditional methods.

Snapshot printers work slowly (a printout can take between two and four minutes, on average) and generally create prints no larger than a standard 4-by-6-inch snapshot. Also, because they spray so much ink on the paper, it can take several minutes for a printout to dry, so smearing can be a problem. Still, they give digital photography enthusiasts a way to print and display their photos in hard-copy form.

Plotter

A plotter is a special kind of output device. It is like a printer because it produces images on paper, but the plotter is typically used to print large-format images, such as construction or engineering drawings created in a CAD system.

Figure: Plotter

Early plotters were bulky, mechanical devices that used robotic arms, which literally drew the image on a piece of paper. Table plotters (or flatbed plotters) use two robotic arms, each of which holds a set of colored ink pens, felt pens, or pencils. The two arms work in concert, operating at right angles as they draw on a stationary piece of paper. In addition to being complex and large (some are almost as big as a billiard table), table plotters are notoriously slow; a large, complicated drawing can take several hours to print.

A variation on the table plotter is the roller plotter (also own as the drum plotter) which uses only one drawing arm but moves the paper instead of holding it flat and stationary. The drawing arm moves side to side as the paper is rolled back and forth through the roller. Working together, the arm and roller can draw perfect circles and other geometric shapes, as well as lines of different weights and colors.

In recent years, mechanical plotters have been displaced by thermal, electrostatic, and ink jet plotters, as well as large format dye-sub printers. These systems, which also produce large-size drawings, are faster and cheaper to use than their mechanical counterparts. They can also produce full- color renderings as well as geometric line drawings, making them more useful than standard mechanical plotters.

Speakers

Microphones are now important input devices, and speakers and their associated technology are key output systems which produce audio sound as output. Today, when we buy a multimedia PC, we receive a machine that includes a CD-ROM (or DVD) drive, a high-quality video controller with plenty of video RAM, speakers, and a sound card.

Generally speakers are used when a mass of people are to be addressed or when music is to be heard around the room. Speaker volume can be adjusted as per the requirement. Speakers also consume less electricity. In the casing, port of speakers can be found. Speakers normally has left and right speakers, they can be adjusted as to listen sound from only one left or right speaker of from both. Speakers can also be used while talking with other people using the Internet or some other technology.

Speakers are usually in a group of two and come in various sizes and shapes. We can listen to songs which are stored on the hard disk of the computer through the speaker. Speakers are used with a computer system to produce output in the form of sound. Some computer games and educational CD’s can be played and understood only when the sound is heard. For that purpose, speakers must be attached with the computer. Speakers are helpful for blind people, who can hear the sound but cannot see the information (output) on the monitor.

The speakers attached to these systems are similar to those we connect to a stereo. The only difference is that they are usually smaller, and they contain their own small amplifiers. Otherwise, they do the same thing any speaker does: they transfer a constantly changing electric current to a magnet, which pushes the speaker cone back and forth. The moving speaker cone creates pressure vibrations in the air-in other words, sound.

Figure: How a speaker creates sound

The more complicated part of the sound output system is in the sound card. The sound card translates digital sound into the electric current that is sent to the speakers. Sound is defined as air pressure varying over time. To digitize sound, the waves are converted to an electric current measured thousands of times per second and recorded as a number. When the sound is played back, the sound card reverses this process, translating the series of numbers into electric current that is sent to the speakers. The magnet moves back and forth with the changing current, creating vibrations.

With the right software, we can do much more than simply record and play back digitized sound. Sound editing programs provide a miniature sound studio, allowing us to view the sound wave and edit it. In the editing, we can cut bits of sound, copy them, and amplify the parts we want to hear more loudly; cut out static; and create many exotic audio effects.
1.9 Software

Introduction

If you are working on a computer, you need the components, hardware and software for its proper functioning. By software, we mean computer instructions or data. Anything that can be stored electronically is computer. The storage devices and display devices are hardware.

Software and hardware are used as both nouns and adjectives. For example, you can say the problem lies in the software which means that there is a problem with the program or data not with the computer itself. You can also say, “It is a software problem.”

The distinction between software and hardware is sometimes confusing because they are so integrally linked. Clearly, when you purchase a program, you are buying software. But to buy the software, you need to buy a floppy or CD-ROM (hardware) to record that software.

Note: Other than software and hardware, there is something called firmware. Firmware is a software stored in Read Only Memory (ROM) or programmable ROM (PROM). It is easier to change than hardware but harder than software stored on disk. Firmware is often responsible for the behaviour of a system when it is first switched on. A typical example would be a “monitor” program in a microcomputer which loads the full operating system from disk or from a network and then passes control to it.

Software Definition

A computer is a hardware and it is useless unless it is provided with the necessary software. Therefore, all computer users should be aware of the basic software concepts besides hardware. A software is a program or set of instructions which is required to use the computer. Many types of software are available for various applications. The software development field is so advanced that day-by-day existing software are becoming outdated and new software are coming in the market. So, one should be aware of the latest developments in the software industry.

Classification of Software

Software are broadly classified into the following two types:

• System software – includes the operating system and all the utilities that enable the computer to function.

• Application software- includes programs that do real work for users. For example, word processors, spreadsheets, and database management systems fall under the category of application software.

Figure: Software Classification

As mentioned above, software can be divided into two general classes: system software and applications software. Systems software consists of low-level programs that interact with the computer at a very basic level. This included operating systems, compilers, and utilities for managing computer resources. In contrast, application software (also called end-user programs) includes database programs, word processors, and spreadsheets.

System Software vs. Application Software

In practice, the difference between system and application software is not always straightforward. Some programs, such as those used to burn DVDs, were originally viewed as utility programs. Today, these programs typically contain a variety of additional features, such as the ability to organize and play music and other media files, transfer videos and digital photos to a computer, edit videos and photos, create DVD movies, copy CDs and DVDs, and create slide shows. Consequently, these programs now fit the definition of application programs more closely. On the other hand, system software today typically contains several application software components. For example, the Microsoft Windows operating system includes a variety of application programs including a Web browser, a calculator, a calendar program, a painting program, a media player, a movie making program, an instant messaging program, and a text editing program. A program’s classification as system or application software usually depends on the principal function of the program, and the distinction between the two categories is not always clear cut.

System Software

Software that is required to control the working of hardware and aid in effective execution of a general user’s applications are called System Software. This software performs a variety of functions like file editing, storage management, resource accounting, Input/ Output management, database management, etc. The purpose of the system software is to make the use of computer more efficient and easier. System software allows the users to communicate with hardware system and allows the users write their own program without knowing the internal structure of hardware. System software also provides the basis for application programs. System software is usually supplied by the manufacturer with the computer.  Some of the examples of system software are DOS (Disk Operating System), Windows, BASIC, COBOL and PC TOOLS.

Types of System Software

System software can be further categorized into the following three types:

• System management software (Operating systems, Operating environments)

• System development software (Language translators, Application generators, CASE tools)

• System software utilities

Operating System

A computer is a complex system. However, it is required that a person with minimal technical skills should be able to use a computer. This is made possible by the operating systems of the computer.

An operating system is a system software, which is set of specialized programs that are used to control the resources of a computer system. Various resources are memory, processor, file system and I/O devices. It is an essential component of the computer system. It is the program running at all times on the computer. Operating systems and computer architecture have a great deal of influence on each other. To facilitate the use of the hardware, operating systems were developed. An operating system is also known as master control program, resource manager and monitor.

An operating system manages and coordinates the activities taking place within the computer and it is the most critical piece of software installed on the computer. It boots the computer, launches application software, and ensures that all actions requested by a user are valid and processed in an orderly fashion. For example, when you issue the command for your computer to store a document on your hard drive, the operating system must perform the following steps:

1) make sure that the specified hard drive exists,

2) verify that there is adequate space on the hard drive to store the document and then store the document in that location, and

3) update the hard drive’s directory with the filename and disk location for that file so that the document can be retrieved again when needed.

In addition to managing all of the resources associated with your local computer, the operating system also facilitates connections to the Internet and other networks.

In general, the operating system serves as an intermediary between the user and the computer, as well as between application programs and the computer system’s hardware (see Figure). Without an operating system, no other program can run, and the computer cannot function. Many tasks performed by the operating system, however, go unnoticed by the user because the operating system works in the background much of the time. Some of the common operating systems are DOS, Windows, Mac OS, Unix, Linux etc.

Figure: Operating System acting as an interface with both application programs and users

Goals of Operating System

Ø  Make computer system convenient to use.

Ø  Managing computer system resources in an efficient manner.

 

Functions of Operating System

Even the simplest operating system in a minicomputer or mainframe performs a number of resource management tasks or functions. These functions include processor management, device management, memory management, command interpretation, security and communication.

Processor Management

A process is a program in execution. During execution a process needs certain resources such as CPU time, memory space, files Input/ Output devices. (At a particular instance of time a computer system normally consists of a collection of process). The process management module or an operating system takes care for the creation and deletion of process scheduling of various system resources to the different processes scheduling of various system different process requesting them and providing mechanism for various for synchronization and communication among process. Processor management, that is assignment of processors to different tasks being performed by the computer system.

Device Management

A computer system consists of several Input/ Output devices such as terminal, printer, disk and tape. The device mismanagement module of an operating system operating system takes care of controlling all the computer’s Input/ Output devices. It also provides an interface between the devices and the rest of the system that is simple and easy to use.

Memory Management

To process the job, required data and job must be loaded into the memory. Function of an operating system is to locate memory in such a way that it improves the CPU utilization ans system efficiency.

Command Interpretation

As a user communicates with computer system using specified set of commands, any command given by the user first interpreted by the operating system then appropriate action is taken.

Security

It provides provision for security so that system is safe from unauthorized access i.e., using passwords.

Communication

It provides efficient and easy mean of communication between user and system.

Performance Evaluation

The efficiency of an operating system and the overall performance depends on the following factors:

1. Throughput

It is measured as total work done by system per unit time. Throughput depends not only on the efficiency of the system but also depends on the job to be performed.

2. Turnaround Time

It is measurement of time elapsed between job submission and job completion.

3. Response Time

It is measurement of time elapsed between job submission and first job response produced.

Types of Operating System

The various types of operating system are as follows:

1. Batch processing
2. Single user
3. Multi-user
4. Multi-tasking
5. Multi-programming
6. Multi-processing
7. Time sharing
8. Real time

Batch Processing Operating System

Batch processing system is also known as off line or sequential or stacked processing system. It is one of the oldest operating system. In this operating system, jobs with similar need batched together by operator and run as a group on a computer system. Users cannot directly interact with the system, just prepared job and submit it to operator. When output produced it is submitted to appropriate user. The major job of batch operating system is to transfer control automatically from one job to another. It is appropriate for executing large job that need little interaction.

Advantages

ü  User / Customer need to wait in queue

ü  Huge Amount of a data need to be processed efficiently.

ü  It reduces idle lime of a computer because operator intervention is not required in automatic job-to-job transition.

Disadvantages

ü  It reduces timeless in some cases

ü  Priority scheduling is difficult to achieve.

ü  Turnaround time increases in some cases.

Single-user Operating System

These operating systems allow only one user to operate at a time i.e., DOS. DOS is the most popular single user operating system. These operating systems are mainly used on personal computers. In DOS we cannot run another program at same time. For this we will have to close the first program, only then we would be able to work on another program or software. Windows 95, Windows 98 are single user operating system but they support multi-tasking and multi-processing facilities.

OS

User Program

        Memory

Multi-user Operating System

It allows simultaneous access to a computer system through two or more terminals. A dedicated transaction processing system such as railway reservation system that supports hundreds of terminal under control of a single program is an example of multi-user operating system. Multi-processor operation without multi-user can be found in operating system of some advanced personnel computers and in real system. e.g., UNIX, XENIX. 1t is useful in a field where simultaneous access to computer system is required i.e., railway reservation system etc.

Multi-tasking Operating System

In multi-tasking, two or more program's can be executed by one user concurrently on the same computer with one central processor. You may write a report on your computer with one program while another program plays a music CD.

To do this work the operating system directs the processor to spend a predetermined amount of time executing the instruction for each program one at a time. Thus a small part of the first program is processed and then the processor moves to the remaining programs one at a time, processing small part of each program, this cycle is repeated until the processing is complete. These operating system support simultaneous processing of several tasks i.e., Windows 95, Windows 98, Windows 2000 etc.

Multi-programming Operating System

In batch operating system job batches are stored in memory for processing. The operating system picks one job and executes it. Eventually jobs have to wait for some Input/ Output operation. That CPU sits idle for that time hence system performance degrades. Multiprogramming increase CPU utilization by organizing jobs such that the CPU always has one job to execute. It is possible by allowing switching between jobs. In multiprogramming operating system more than one job resides in main memory and hence the memory is utilized. The CPU picks one job and starts executing it, when the job requires to perform Input/ Output operation, the CPU does not sit idle and picks the next job and start executing its instruction, in this way a single CPU is in demand all the time and hence it is fully utilized.

Multi-processing Operating System

Multi-processing is a processing done by two or more computers or processors linked together to perform work simultaneously and precisely at the same time. This can entail processing instruction from different programs or different instructions within the same program at once. Two possible approaches to multiprocessing are co-processing and parallel processing. In co-processing the controlling CPU works together with a specialized microprocessor called coprocessor each of which handles a particular task such as creating display-screen graphics or performing high-speed mathematical calculations. Many microcomputer systems have co-processing capabilities. In Parallel processing several full-fledged processors work together on the same tasks, sharing memory. Parallel processing is often used in large computer systems designed to keep running if one of the CPU fails.

Time Sharing 0perating System

In time sharing operating system the many users can operate computer system simultaneously. The CPU executes multiple jobs and switches between them so frequently that the user may interact with each job while it is running. CPU time is divided between users that use it one-by-one. It provides an interactive online communication between user and the system. Time sharing systems are expensive and more complex than rnulti-programming operating systems.

Figure: The process state diagram for time sharing system

Real Time Operating System

The real time operating system has well defined, fixed time constraint. Processing must be done within fixed time constraint. This operating system provides quick response time. A real time operating system is considered to function correctly only if it returns the correct result within any time constraint.

Real time operating systems are used when there are rigid time requirement on the operation of a processor or the flow of data, and thus is often used as control device in dedicated, application. Systems that control scientific experiments, medical imaging systems, industrial control systems, and some display systems are real-time systems.

There are two types of real time operating systems:

1. Hard real time operating system
2. Soft real time operating system

Hard real time operating assured that critical tasks completes on time. This goal require that all delays in the system be bounded, from the retrieval of stored data to time that it takes the operating system to finish any request made to it. On the other hand, soft real time operating system is a less-restrictive real time operating system, where a critical real-time task gets priority over other tasks, and retains that priority until it completes. Soft real time operating systems have more limited utility than hard real time operating systems.

Utility Software

Utility software is a computer program that performs a very specific task, usually related to managing system resources. It is also called system support software or service program, which provide useful services to the user of the computer.  Utility programs are programs- that enhance or extend the operating system’s capabilities or which simply offer new feature not provided by operating system itself.

Utility software assists in maintaining, managing, and protecting computer system resources. In fact, as operating systems have developed, they have incorporated features that were originally found in separate utility programs, such as disk maintenance utilities. Utilities are used to merge and sort sets of data, keep track of computer jobs being run, and perform other important routine tasks. Utility programs often come installed on computer systems; a number of utility programs can also be purchased.

The following are common utilities that protect computer systems and keep them running smoothly:

• Defragmentation and disk utilities: Maintain files on disk and arrange them in a contiguous manner for fast access

Figure: Disk Defragmenter

• Backup utilities: Safeguard files by creating backup copies

Figure: Backup Utilities

• Security software: Search for and remove viruses and spyware from computers, and guard against attacks; must be updated frequently

                                       Figure: Security Software

• System restore: Restore computer to a previous state, if a problem occurs, without losing personal data files.

Figure: System Restore

• Spam and pop-up blockers: Save users time by eliminating unwanted junk mail and ads

 

Figure: Spam and pop-up blockers

• Compression utilities: Output a shorter stream or a smaller file by compressing them.

 

Figure: Compression Utility

• Network managers: Checks network, log events and check data transfer.

  

Figure: Network Manager

• Windows cleaners: Remove unwanted programs and leftover traces of programs from the system, and maintain the Windows Registry for smoother OS operation

Figure: Windows Cleaner

• Parental controls: Filter Internet content and place restrictions on computer use for the safety of minors

Figure: Parental Control

A number of utilities are designed to assist users in managing and transferring files:

• File management utilities: Provide tools for copying, deleting, renaming, and organizing files
• File compression utilities: Allow files to be bundled together into one compressed file to save storage space and allow for easier transfer
• CD/DVD burners: Copy and store files on CDs and DVDs
• File transfer utilities: Move and share files across networks
• Search utilities: Find files

Major utility software are given below:

ü  Device driver

ü  Antivirus

Device Driver

Just as the OS manages the hardware inside the computer, it also manages and coordinates the use of input and output devices and other peripheral equipment. Today’s computers usually have keyboards, pointing devices, printers, and display screens. Some users have other peripheral devices that can be attached as well, like game controllers, Webcams, and iPods. The operating system must manage all of these devices.

Any device that connects to a computer includes associated software called the device driver that must be installed in order for the operating system to recognize and communicate with the device. A device driver is a computer program that allows higher level computer programs to interact with a hardware device. For example, suppose you get a fancy new wireless mouse with extra buttons for controlling the volume on your media player. In order for the operating system to understand the unique controls that this mouse has, the device driver must be installed. The main purpose of device driver is to simplify programming by acting as a translator between a device and the applications or operating systems that use it.

The device driver is designed by the company that manufactures the peripheral device and is written for a particular operating system. For example, if you upgrade from one version of Windows to another, you may find that you need to download new device drivers for some of your devices in order for them to be recognized by the new OS. Device drivers can typically be found and downloaded at the Web site of the manufacturer. As with other software, it is useful to download and install upgrades for your device drivers when and if they become available.

Device drivers often come on a CD packaged with the peripheral device, or they can be downloaded from the manufacturer’s Web site. Most operating systems today look for and recognize new devices each time the computer boots. If a new device is found, the operating system typically tries to install the appropriate driver automatically in order to get the new hardware ready to use—a feature called Plug and Play. Because USB and FireWire devices can be connected to a computer when the computer is running, those devices are recognized and configured, as needed, each time they are plugged in to the computer.

Once a device and its driver have been installed properly, they usually work fine. If the device driver file is deleted, becomes corrupted, or has a conflict with another piece of software, then the device will no longer work. Usually, the operating system detects problems like this during the boot process and notifies the user, and then tries to reinstall the driver automatically. If the operating system is unable to correct the problem, the user can reinstall the driver manually. You may also need to update or reinstall some device drivers if you upgrade your operating system to a newer version. To keep your system up-to-date, many operating systems have an option to check for operating system updates automatically—including updated driver files—on a regular basis. Enabling these automatic updates is a good idea to keep your system running smoothly and protected from new threats.

Device Driver Applications

Device driver are used for interfacing with:

Printer	Sound Card
Video Graphics Card	Image Scanner
Network Card	Game Controllers
Digital Camera	Webcams
Video Camera	iPods/ iPhone

Antivirus

A computer virus is a software program that is designed to cause damage to the computer system or perform some other malicious act, and spyware is a software program installed without the user’s knowledge that secretly collects information and sends it to an outside party via the user’s Internet connection. Other security concerns today include phishing schemes that try to trick users into supplying personal information that can be used for credit card fraud, identity theft, and other criminal acts. Because of these threats, it is critical that all computer users today protect themselves and their computers.

There are many security programs available, such as antivirus programs and antispyware programs (that protect against malicious software being installed on your computer) and firewall programs (that protect against someone accessing your computer via the Internet or a wireless connection). Increasingly, operating systems are including security software integrated into the operating system. For instance, recent versions of Windows include Windows Firewall and Windows Defender (an antispyware program).

Antivirus is a type of utility software that looks for and removes viruses, Trojan horses, worms, and bots. Some antivirus software also scans for spyware, although several security software publishers offer spyware detection as a separate module. Antivirus software is included in security suites or can be purchased as a standalone module. Antivirus software is available for all types of computers and data storage devices, including handhelds, personal computers, USB flash drives, and servers. Some of the popular antivirus are Norton, Panda Antivirus Pro, Kaspersky, MacAfee, Avast Pro, Avira Antivir, AVG, ESET Nod 32 etc.

Modern antivirus software attempts to identify malware by searching your computer’s files and memory for virus signatures. A virus signature is a section of program code, such as a unique series of instructions, which can be used to identify a known malicious program, much as a fingerprint is used to identify an individual. Antivirus software scans for virus signatures in programs, data files, incoming and outgoing e-mail and attachments, and inbound instant message attachments. Antivirus software can also watch for unusual activity such as a considerably large number of e-mail messages being sent out from your computer. Most antivirus programs can also scan for virus signatures in zip files, which is important when downloading zipped software and receiving zipped e-mail attachments.

Antivirus can protect computer to a large extent from virus, worms and other malicious programs but it may not be the ultimate solution. The users must take certain precautions on their own to make their computer system free from viruses. They must choose the proper antivirus software and update it regularly. Infected Pen Drive or CD/DVD must be avoided as much as possible and unnecessary Web Sites which may spread virus should not be visited.

Application Software

Application software is computer program that perform a specific function directly for the users. It helps the user to work faster, more efficiently and more productively. Application software are developed and supplied by software companies. Application software enables a computer to perform a specific task such as handling financial accounting, processing words, preparing exam result, producing bills, manipulating images and videos, etc. To write a program for financial accounting or other application the programmer does not need to control the basic circuit of a computer. Application software does its tasks with the help of operating system. There are two types of application software. They are:

1. Customized or Tailored Software
2. Packaged Software

a. Customized or Tailored Software

Customized or Tailored software is the application software which is designed to fulfill the specific requirements of an organization, office or individual. Customized software is developed on the demand of customer by a software contractor. SLC Result Processing Software, Hospital Management Software, School Management Software, Bill Processing Software, Air Ticket Reservation Software, Banking software etc. are examples of customized software.

b. Packaged Software

Packaged software is the readymade software designed and developed for all general users to perform their generalized tasks. These are the software which are produced by development organization and sold on the open market to any customer who is able to buy them.

Some of the popular packaged software is given below:

Word Processing Software: used for creating, editing, viewing, formatting, storing and printing documents. Examples:- MS-Word, Aldus PageMaker, Word Perfect, etc.

Electronic Spreadsheet Software: used for keeping accounts and doing numeric data analysis. The worksheet can be viewed as a matrix of rows and columns. The intersections of row and column in worksheet are called a cell. These packages are very useful for analyzing budgets, cash flow, profitability and many similar problems. Examples:- MS-Excel, Lotus 123, etc.

Presentation Programs: used for creating and presenting electronic slide shows. Example:- MS PowerPoint, Lotus Freelance Graphics, Harvard Presentation Graphics etc.

Database Management System Software: used for managing large volumes of data. A typical organization may need to maintain databases on customers, suppliers, employees etc. on the computer. Examples:- MS-Access, Dbase, Sybase, SQL Server, Oracle, etc.

Graphics Software: used for creating, editing, viewing, storing and printing images, graphs and pictures. Examples:- CorelDraw, Paintbrush, Photoshop etc.

Multimedia Software: used for designing multimedia. Examples:- 3D Max, Maya, Flash, PowerPoint, Windows Media Player, etc.

Entertainment Software: used as an entertainment tool. A good example of such an application is a computer video games.

Personal assistance software: allows us to use personal computers for storing and retrieving our personal information and planning and managing our schedules contacts, financial and inventory of important items.

Word Processor

Word processing software (also called a word processor) is an application that provides extensive tools for creating all kinds of text-based documents. Word processors use a computer to create, edit, and print documents. Word processors are not limited to working with text. Word processors enable you to add images to documents and design documents that look like products of a professional print shop. Of all computer applications, word processors are the most common.

To perform word processing, you need a computer, the word processing software (word processor), and a printer. A word processor enables you to create a document, store it electronically on a disk, display it on a screen, modify it by entering commands and characters from the keyboard, and print it on a printer.

The great advantage of word processing over using a typewriter is that you can make changes without retyping the entire document. If you make a typing mistake, you simply back up the cursor and correct your mistake. If you want to delete a paragraph, you simply remove it, without leaving a trace. It is equally easy to insert a word, sentence, or paragraph in the middle of a document. Word processors also make it easy to move sections of text from one place to another within a document, or between documents. When you have made all the changes you want, you can send the file to a printer to get a hardcopy. Some of the commonly used word processors are Microsoft Word, WordStar, AmiPro, Professional Write, Apple Pages, Corel WordPerfect, Lotus WordPro, Sun Microsystems Write etc.

The features available on today’s word processors are stunning. All of the common features you would expect are included, such as easy text entry and formatting, and the capability to develop attractive tables, check spelling and grammar, and generate footnotes and endnotes. You can create automatically numbered or bulleted lists and insert photos, graphics, and drawings. Today’s word-processing programs also have sophisticated document-processing features such as generating a table of contents at the beginning of the text and an index at the end. Word 2007 and Word 2010 include intuitive features that provide easily accessible tools for a variety of document styles. New features in Word 2010 include a navigation pane that provides a birds-eye view of a document, a powerful document search tool, and impressive graphics tools for creating SmartArt graphs and visualizations and image and font effects.

Word-processing programs can be used with a team or group of people collaborating on a project. The authors and editors who developed this book, for example, used the Track Changes and Reviewing features of Microsoft Word to track and make changes to chapter files without overwriting each other’s work. You can insert comments in or make revisions to a document that a co-worker can review and either accept or reject. Microsoft Office Web Apps, Google Docs, and other online word processors provide an excellent environment for collaboration, allowing individuals to work on the same document simultaneously. Software that functions to support group collaboration is sometimes referred to as groupware.

Advantages of Word Processing

The advantages of word processing are as follows:

1. Increased office efficiency resulting in improved secretarial support for all word originators (including executives).
2. Higher quality output resulting from advanced equipment.
3. Improved human resource utilization with better control and supervision of secretarial personnel through a word processing centre.

In particular, improved productivity is obtained by:

1. Reduced retyping time for error-free hard copy.
2. Facilitation of document revision and change before committing to paper.
3. Faster output speed.
4. Reduction in amount of proof reading required.
5. Elimination of stationery wastage.

Applications of Word Processing

The applications of word processing are given below:

• Text editing and publishing documents.
• Checking spelling and grammars of document.
• Web publishing, mail merging and image insertion.
• Mathematical calculations and macro handlings.
• Formatting and editing documents.
• Colouring and numbering documents pages.
• Official tasks such as create save, close, open etc.

Spread Sheets

A spreadsheet is a table of values arranged in rows and columns. Each value can have a predefined relationship to the other values. If you change one value, therefore, you may need to change other values as well.

Spreadsheet applications (often referred to simply as spreadsheets) are computer programs that let you create and manipulate spreadsheets electronically. It is a software tool for entering, calculating, manipulating and analyzing sets of numbers. Spreadsheets have a wide range of uses- from family budgets to corporate earnings statement. In a spreadsheet application, each value sits in a cell. You can define what type of data is in each cell and how different cells depend on one another. The relationships between cells are called formulas, and the names of the cells are called labels.

Once you have defined the cells and the formulas for linking them together, you can enter your data. You can then modify selected values to see how all the other values change accordingly. This enables you to study various what-if scenarios.

There are a number of spreadsheet applications in the market like Microsoft Excel, Lotus 1-2-3, Apple Numbers, and Corel Quattro Pro. These applications support graphic features that enable you to produce charts and graphs from the data.

Some spreadsheets are multidimensional, meaning that you can link one spreadsheet to another. A three-dimensional spreadsheet, for example, is like a stack of spreadsheets all connected by formulae. A change made in one spreadsheet automatically affects other spreadsheets.

Spreadsheet programs have many built-in functions for science and engineering, statistics, and business. The science and engineering functions include sine, cosine, tangent, degrees, maximum, minimum, logarithms, radians, square root, and exponents. The statistical functions include correlation, statistical testing, probability, variance, frequency, mean, median, mode, and much more. The business functions include depreciation, present value, internal rate of return, and the monthly payment on a loan, to name a few. Spreadsheets also provide methods of displaying data in an attractive and meaningful way. Microsoft Excel provides dozens of types and styles of graphs that can illustrate numeric information visually. It also provides automated tools for formatting numeric information in any one of a wide variety of attractive tables.

Spreadsheets include many of the tools associated with word processing, including the ability to format fonts and text alignment, insert images, and check spelling. Microsoft Excel 2010 also includes the group collaboration tools provided in Word 2010.

Optimization is another powerful feature of many spreadsheet programs. Optimization allows the spreadsheet to maximize or minimize a quantity subject to certain constraints. For example, a company that produces dog food might want to minimize its costs while meeting certain nutritional standards. Minimizing costs becomes the objective and the nutritional standards are the constraints. An optimization feature can determine the blend of dog food ingredients that minimizes costs and meets the nutritional requirements. This is just one of many examples of the use of optimization in spreadsheets. Because of the power and popularity of spreadsheet optimization, some colleges and universities offer complete courses based on Solver in the Microsoft Excel spreadsheet. Most of these courses are in engineering and business schools.

Common Features of Spreadsheet Package

• Support for a large number of cells
• Support for addressing a range of cells by the address of the endpoint cells
• Support for different types of cell data (such as label, numeric value, formula, and date & time)
• Support for use of relative and absolute cell addresses in formula
• Support for a wide range of commands
• Support for displaying numeric data in the form of graphs and charts.

Uses of Spreadsheet Package

• Maintaining and analyzing inventory, payroll, and other accounting records by accountants.
• Preparing budgets and bid comparisons by business analysts.
• Recording grades of students and carrying out various types of analysis of the grades by educators.
• Analyzing experimental results by scientists and researchers.
• Tracking stocks and keeping records of investor accounts by stockbrokers.
• Creating and tracking personal budgets, loan payments, etc. By individuals

MS Excel is the example of spreadsheet program which is used by millions of people nowadays. It runs in simple operating system and was developed by Microsoft Company. It has large numbers of features such as mathematical and logical calculation and has also some features of word processing packages too. It is used for official task for simple mathematical and logical calculations.

Excel is organized to allow calculations in a tabular form. It is similar to the way we would lay out the same calculations on a paper with a pencil. The “paper” is called a worksheet in Excel and is divided into a rectangular grid as rows and columns. The intersection of a row and column is referred to as a worksheet cell. These cells contain all the data, text and formulas that comprise a calculation and its associated documentation.

Rows are labelled by numbers (1, 2, 3...) and columns are labelled by letters (A, B, C... AA, AB, AC...). Cells are then labelled with both the column letter(s) and row number(s) in that order. A cell is selected (highlighted) by clicking the cursor over it. Only one cell can be selected at a given time and this cell is referred to as the active cell.

Presentation Tool

Presentation tools are used to produce a series of slides- single screen images that contain a combination of text, numbers, and graphics (such as charts, clip art or pictures), often on a colorful background. It supports formal presentations by providing “slides” that can be used to accompany and embellish a live presentation or to present the material without the use of a human speaker.

Presentation software is extremely useful for transmitting information to professional groups and audiences that can vary from a few people to thousands. Physicians and medical personnel use presentation software to show the results of medical research at conferences. Forest service consultants use presentation software to describe new forest management programs, and businesses almost always use presentation software to present financial results or new initiatives to executives and managers. Because of its established use in most professions, many colleges and departments require students to become proficient with presentation software.

Most presentations created with presentation software, such as Microsoft PowerPoint, Apple Keynote, Lotus Freelance Graphics, and Harvard Presentation Graphics, consist of a series of slides. Each slide can be displayed on a computer screen, printed as a handout, or (more commonly) projected onto a large viewing screen for audiences. Powerful built-in features allow you to develop attractive slides and complete presentations. Slides typically include visual aids such as graphs and images that allow an audience to better understand the topic being presented. Slides may be animated with moving objects and transitions, and may include music and video. You can select a template for a type of presentation, such as recommending a strategy for managers, communicating bad news to a sales force, giving a training presentation, or facilitating a brainstorming session. The presentation software takes you through the presentation step by step, including applying color and attractive formatting. Of course, you can also custom design your own presentation.

Features of Presentation Software

• Allows you to insert slide anywhere in the presentation, at the beginning, middle or end.
• Allows you to delete any slide of the presentation.
• Allows you to view your work in different view options like normal, outline, slide, slide sorter, slide show etc.
•  Allows cut and paste slides in any order.
• Allows duplication content or slide
• Allows you to add speaker notes to a presentation.
• Allows you to display the presentation designed in a slide show system. (View Slide Feature)
•  Allows animations and/or sounds manipulations on objects in the slide.
• Simple Find and Replace, and text editor features.
• Allows you to change and use different font faces, styles, and effects
• Allows you to add features for slide like footnotes, cross references, advanced navigation system, headers, footers etc.
• Allows you to add macros for interactive features
  
  

Microsoft PowerPoint is one of the most popular and powerful presentation tools. It helps one to build, print and deliver presentations. One has several options for the delivery of a presentation but you only have to develop it once. One can print slides (each screen of information), handouts, notes pages, prepare for 35mm slides, or deliver an on-screen presentation. Only an on-screen presentation allows one to use the full range of the features of PowerPoint.

As we develop a PowerPoint presentation, it is important to remember that we should not try to include every piece of information we wish to deliver. PowerPoint slides should contain brief, concise, descriptive phrases that will help us remember what we want to present and to serve as a reminder for our audience. The most common mistake made by novice PowerPoint developers is to stuff too much information on each slide.

Database Management Software

Database-management software is an application program that is used to store, manipulate, and manage data in order to find and present useful information. Databases can be used to store large tables of information. Each table can be related. For example, a company can create and store tables that contain customer information, inventory information, employee information, and much more. Assume a customer decides to place an order for two flash drives, one for herself and one for a friend, by calling a sales representative with whom she has worked in the past. The sales representative can record the customer number, the item number for the flash drive, and the quantity, two in this case. The database management software does the rest. First, the program takes the customer number and goes to the customer table to retrieve the name, address, and credit card information. With the employee number of the sales representative from the customer table, the database management software goes to the employee table to determine any sales commissions that should be paid to the sales representative. Next, the database management system takes the item number for the flash drive and goes to the inventory table to get all the information about the flash drive and make sure that there are at least two in stock. Once all of this is done, the order can be processed and the two flash drives sent to the customer. All of this is done as a result of giving the customer number, item number, and quantity to the database management software. Before database management software existed, processing an order was done manually, requiring a lot of time and potentially making many mistakes.

In addition to order processing, database management software can be used to perform many of the business functions for a small business, including payroll, inventory control, order processing, bill paying, and producing tax returns. Database-management systems can also be used to track and analyze stock and bond prices, analyze weather data to make forecasts for the next several days, and summarize medical research results. At home, we can use database management software to keep a record of expenses, a list of what is in our apartment or home, or a list of the members of a student government organization.

Microsoft Access is designed to support the small databases used at home or in a small business. Larger corporations rely on large database systems, such as Microsoft SQL Server or Oracle, for the millions of records they maintain and manipulate.