Computer Hard Disk Drive

Hard Disk Drive

A hard disc drive (HDD) is an electromechanical data memory device that stores digital data using one or sooner rotating rigid plates coated with magnetic material. Use magnetic storage to perform and recover. . The tracers are attached to a magnetic head, usually arranged on a movable actuator arm, which reads and writes data onto the platter's surfaces. Data is accessed randomly, which means that individual blocks of data can be stored and recalled in any order. HDD is a type of non-volatile storage that keeps data stored even when operating.

Introduced by IBM in 195, [uced] hard drives were the primary secondary storage device for general-purpose computers in the early 1980s. Hard drives maintained this position in servers and personal computers in the modern era. However, a large number of personal computing devices, such as cell phones and tablets, rely on Flash products. Historically, more than 224 companies have produced hard drives, although most drives are manufactured by Seagate, Toshiba, and Western Digital following extensive industry consolidation. HDD dominates the amount of storage produced (discount per year) for servers. Although production is gradually increasing, sales revenue and drive shipments are declining because solid-state drives (SSDs) have higher data transfer rates, higher area storage density, better reliability, and a much lower latency and Access time. 

SSD revenue, most of which uses NAND, is slightly higher for HDD. As of 2017 2017, hard drives had more than double revenue from flash storage products. Although SSDs cost four to nine times more per bit, they are turning HDDs into applications where speed, power consumption, small size, high capacity, and durability are important. The cost per bit for SSDs is falling, and the price premium on HDDs has dropped.

The main features of HDD are its capability and performance. Computer operating systems, and possibly built-in redundancy for error correction and recovery. There is also confusion about storage capacity, as HDD manufacturers claim that capacity is in decimal gigabytes (power of 10), while some operating systems report capacity in binary gigabytes, resulting in lower numbers than advertised. The performance is specified by the time (average reach time) required to move the track or cylinder, adding time to move the desired area under the head. and finally, the speed with which data is transmitted (data rate).

The two most common form factors for modern hard drives are, 3.5 inches for desktop computers, and 2.5 inches, mainly for laptops. The hard drive connects to the system using standard interface cables, such as PATA (parallel ATA), SATA (serial ATA), USB, or SAS (serial connected SCSI) cables.

Hard Disk Drive:-

Disk Storage 350, IBM's first production hard drive, was shipped in 1957 as a component of the RAMAC IBM 305 system. It was roughly the size of two mid-size refrigerators and stored five million six-bit characters (3.75 megabytes) on a stack of 50 discs.  The 350 had a single arm with two reed / right heads, one up and one down, moving horizontally through a pair of decks and vertically from one deck to another set. 

In 1962, the IBM 350 was replaced by an IBM 1301 disk storage unit,  consisting of 50 platters, each of the 8 inches thick and 24 inches in diameter. [3 IBM] While IBM 350,  355,  35300 [35] and 1805 used only two reads / write heads per hand, 1301 used the same head array ("Comb"). Used, per plate, moves horizontally as a unit. Cylinder mode read/write operations were supported, and the head flew approximately 250 micro inches (about 6 μm) above the surface of the platter. The movement of the head array relies on a binary additive system of hydraulic actuators that ensures repeatable positioning. Cabinet 1301 was placed next to each other, the size of three domestic refrigerators, storing the equivalent of approximately 21 million eight-bit bytes. The access time was about a quarter of a second.

Users can purchase additional packages and swap them as needed, such as magnetic tape reels. Later models of removable package drives, from IBM and others, became the norm in most computing facilities and reached a capacity of 300 megabytes in the early 1980s. Non-removable hard drives were called "drives". Fixed disk ".

Some high-performance hard drives were built with one head per track, for example, Burrows 475 in 1964, IBM 2305 in 1970, so no time wasted in physically moving the head on one track and only latency. The time was for the desired data block to rotate under the head position. Known as fixed-head or head-on-track disk drives, they were very expensive and are no longer in production. 

In 1973, IBM introduced a new type of HDD called "Winchester". Its main distinguishing feature was that when the unit was shut down, the disc heads did not completely move from the stack of disc platters. Instead, the head was allowed to "land" on a particular area of ​​the disk's surface as it resumed when the disc was subsequently turned. This greatly reduced the cost of the head drive mechanism, but prevented the removal of only the disk from the drive, as was done with the disk pack of the day. Later, the "Winchester" drive abandoned the concept of removable media and returned to non-removable platters.

Like the first removable package unit, the first "Winchester" units had 14-inch (360 mm) diameter dishes. A few years later, designers were exploring the possibility that physically small plates could offer advantages. The units appeared with eight-inch non-removable platters, and then the units used a 5 1⁄4 in (130 mm) form factor (equivalent to a mounting width used by contemporary floppy drives). The latter were mainly for the personal computer (PC) market.

When the early 1980s began, hard drives were a rare and very expensive add-on feature on PCs, but by the late 1980s, their costs had fallen to the point where they were the standard on all but the cheapest computers.

In the early 1980s, most hard drives were sold to PC users as an additional external subsystem. The subsystem was not sold under the name of the drive manufacturer but under the name of the subsystem manufacturer, such as Corvus Systems and Tallgrass Technologies, or under the name of the PC system manufacturer, such as Apple ProFile. In 1983 IBM PC / XT included a 10MB internal HDD, and later the internal HDDs spread on personal computers.