Hard drive is also known as HDD or hard disk drive or hard disk. It is a non volatile storage device. It stores the digitally encoded data with the help of magnetic surfaces on rapidly rotating platters. HDDs were first introduced in 1956 for IBM general purpose computers.

Embedded systems such as RAIDs, network attached storage (NAS) systems and storage area network (SAN) systems which provide reliable access to large volume of data. These were introduced in 1990s to cover-up the need of large scale, reliable storage devices.

As we all know drive actually means a device which is distinct from its medium like floppy disk drive or floppy disk and tape drive or its tape. Now-a-days hard disk drives are in a perfectly sealed unit except of the vent to maintain the air pressure with fixed media irrespective of the early HDD with removable media.

Hard disk works as it stores the data by magnetizing ferromagnetic material in a particular direction, to represent either of the binary digit, 0 or 1. To read the data back the magnetization is detected of the material.

The typical design of HDD comprises of one or more flat circular disk hold by the spindle. These circular disks are called platters onto which the data is recorded. These platters are made up of non magnetic material and a thin coating of magnetic material is used over it. In the earlier disks the magnetic material used was iron oxide but cobalt based alloy is used in the current disks. It consists of a read-and-write heads which rotates past the platter operated very close over it.

The read-and-write heads helps to detect and modify the magnetization of the ferromagnetic material immediately under it. Each platter have its own read-and-write head, all mounted on a common arm.

Typically the hard drives have two motors, one to spin the disk and one to position the read-and-write head. The platters are rotated at very high speed and in modern disks acceleration at the read-and-write heads reaches 250Gs.

Modern drives make massive use of Error Correcting Codes (ECCs), particularly Reed–Solomon error correction. By this technique, drives store extra bits for each block of data that are firmed by mathematical formulas. All errors are allowed to be fixed by these extra bits only. In 2009, Reed-Solomon is being replaced by low-density parity-check codes (LDPC), in the modern drives. LDPC allows for the highest storage density available as it codes enable performance is very close to the Shannon limit. use your link here

As the hard drive is sealed tightly and rigid they enable much tighter tolerance than in a floppy drive. As well as hard drive can store more data and access and transmit it at much faster rate than the floppy disk drive. The increase in the storage capacity and accessibility of hard disk drives enables the commercial viability of consumer products like digital video recorders and digital audio players which requires large storage capacity.

The way to increase the data storage capacity and throughput is to increase the aerial density and the main way to increase the accessibility means to decrease the access time is to increase the rotational speed, thus reducing rotational delay.

All of the world’s HDD are produced by five major companies: Seagate, Western Digital, Hitachi, Samsung and Toshiba. As the demand for capacities and the products increased, profits became hard to find, so dozens of the former HDD manufacturers merged or closed their divisions or the companies of HDD production.

In 21st century, HDDs are commonly used in gadgets like camcorders, cell phones, digital audio players, digital video players, digital video recorders, personal digital assistants and video game consoles.

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