Hard disk

History of Hard Disk Drive

Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes. They were originally called "fixed disks" or "Winchesters" (a code name used for a popular IBM product). A hard disk drive consists of a motor, spindle, platters, read/write heads, actuator, frame, air filter, and electronics.

The first computer with a hard disk was IBM’s RAMAC, which was used during the 1960 Olympics to calculate sports results. A bit later, in 1962, removable disk packs were developed – a forerunner of the floppy disk. In 1964, the CRC algorithm was introduced. It provided greater security by checking and comparing data before and after it was written to the disk. In 1971, the first 8-inch diskettes came onto the market.

But it wasn’t until the middle of the 1980’s that people began to use hard disks in more standard PC’s, and since then development has surged ahead. The capacity of a standard hard disk has actually become a thousand times greater in the period 1990-2000.

The standard user’s need for disk space (e.g. for digital photos, video and music) has grown in step with this, so that 120-250 GB of disk space or more is normal in many PC’s – a figure which will double over the next few years.

Hard disks are constantly being developed which have greater capacity and speed (the two go together, as we shall see), and there is therefore a constant need for new types of hard disk controllers. The companies leading the development are Maxtor, Western Digital, IBM/Hitachi and Seagate.

The frame mounts the mechanical parts of the drive and is sealed with a cover. The sealed part of the drive is known as the Hard Disk Assembly or HDA. The drive electronics usually consists of one or more printed circuit boards mounted on the bottom of the HDA.

How Hard Disk Works?

Data on a hard disk is stored in microscopic areas called magnetic domains on the magnetic material. Each domain stores either a 1 or 0 value. Similar to a floppy disk, a hard disk records its data in concentric circles or tracks, which are numbered from the outermost edge to the innermost edge of the platter. These tracks are further subdivided into smaller units called sectors which typically store 512 bytes of data each. Zoning may be needed to further optimise the data storage as the outer circumference would normally pack more sector units than the inner circumference.

• When a command is made to store some data on a disk, the following chain of events occurs:
• The data flows into a cache where it is encoded using special mathematically derived formulae, ensuring that any subsequent errors caused by noise can be detected and corrected.
• Free sectors on the disk are selected and the actuator moves the heads over those sectors just prior to writing. (The time it takes the actuator to move to the selected data track is called the "seek" time.)
• Once over the data track, the heads must not write the data until the selected free sectors on that track pass beneath the head. This time is related to the rotation speed of the disk: the faster the speed, the shorter this "latency" period.
• When it's time to write, a pattern of electrical pulses representing the data pass through a coil in the writing element of the recording head, producing a related pattern of magnetic fields at a gap in the head nearest the disk. These magnetic fields alter the magnetic orientations of bit regions on the disk itself, so the bits now represent the data.

When a command is made to read some data on a disk, a similar process occurs in reverse. After consulting the table of stored data locations in the drive's electronics, the actuator moves the head over the track where the chosen data is located. When the correct sectors pass beneath the head, the magnetic fields from the bits induce resistivity changes in the sensitive MR or GMR materials located in the reading elements within the head. These elements are connected to electronic circuits, and the current flowing through those circuits change with the resistivity changes. The current variations are then detected and decoded to reveal the data that had been stored on the disk.

First Hard Disk in the World 

World's First Hard disk - At this time I will show the first hard disk weighing more than 1 ton, a very historic thing in the tech world as well as in the world of IT (Information Technology), Curious any kind of capacity, price, and speed? The picture below is the first hard disk, which was launched in September 1956 with the IBM 305 RAMAC title. The storage capacity of 5 Mb hard drive and is the first computer using a hard disk drive. Heavy hard disk is more than 1 ton.

Specifications:
IBM 305 RAMAC (Random Access Method of Accounting and Control) 1956
1. Capacity: 4.8 MB
2. rotational speed: 1,200 rpm
3. Rent: $ 3,200 per month (1957)
4. Business users first: Chrysler's Mopar Division (1957)
5. The number of units that have been produced: over 1000 units by year 1961

Types of Hard Disks

There are few different types of hard disks, but other than its physical size, the different type of interfaces of the hard disk is main difference.

1. IDE : Integrated Drive Electronics. IDE drives are also known as PATA drives( Parallel advance technology attachment )
2. SATA : Serial advance technology attachment
3. SCSI  (Small Computer System Interface). SCSI is pronounced as scuzzy.
4. SAS : Serial Attached SCSI

IDE PATA Drive

IDE PATA Drive Cable

IDE / PATA (Integrated Drive Electronics Drive / Parallel Advance Technology Attachment Drive)

• IDE/PATA Drives have usually 40 pins.
• IDE/PATA Drives offer 133 MB/sec transfer rate.
• It sends 8 bit data at a time. 
• PATA Cables are used to connect PATA HDD. Two drives can be connected in a single pata cable. One as master and other as slave. The configuration of master and slave is done by different combination of jumpers in the HDD.

SATA DRIVE

SATA Drive Cable

SATA (Serial Advance Technology Attachment Drive)

• SATA Drives have usually 7 pins, 4 pins in pair of two for sending and receiving data and rest 3 pins are grounded.
• SATA Drives offers generally 300MB/sec transfer rate.
• It sends data bit by bit.
• SATA Cables are used to connect SATA HDD. Only one drive can be connected in a single sata cable.

SCSI Disk Drive

SCSI Data Cable

SCSI (Small Computer System Interface Drive)

• SCSI Drives have usually 50 to 68 pins.
• SCSI Drive offers generally 640MB/sec transfer rate.
• This drives are hot swappable. 
• SCSI cables are used to connect SCSI HDD. Maximum of 16 drives can be connected in a single scsi cable. Each hdd have a 8 bytes hexadecimal code known as WWN (world wide name) for its identification in the cable.

SAS(Serial Attached SCSI Drive)

SAS Data Cable

SAS(Serial Attached SCSI Drive) 

• SAS Drives generally offers 805 MB/sec transfer rate.
• This drives are hot swappable.
• SAS Cables are used to connect SAS Drives. Maximum of 128 drives can be connected in a single sas cable.