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What Is a Hard Disk Drive?

Hard disk drive with case removed to show the platters and the read-write head.
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  • Written By: Henry Gaudet
  • Edited By: A. Joseph
  • Last Modified Date: 12 August 2014
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The hard disk drive, or hard drive, is a data storage device used in computers of all sizes as well as other electronic devices that can record information. As a built-in piece of hardware, it also has the advantage of permanence, and information stored will remain available until it is deleted or altered. In a computer, the hard disk drive typically is the largest, fastest storage device available, usually storing essential files such as the operating system and startup programs.

When opened, the hard disk drive resembles a record turntable, with an arm passing over the platter. A closer look will reveal not one disk but a stack of reflective platters, each readable on both sides. The arm is split into layers as well, with the layers passing between platters, meaning that all surfaces of all disks can be read simultaneously. It should be noted that opening the drive will make it unusable, so this should be attempted only if the hard disk drive is already broken.

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Before the invention of the hard disk drive, data storage options were limited to punch cards that were cumbersome and prone to jams or magnetic tape that had to rewind or fast forward to the desired information, slowing performance. In 1956, International Business Machines Corp. (IBM) created the first hard disk drive, allowing data to be accessed quickly and in any sequence desired. In 1973, IBM developed a dual device nicknamed the 30-3,0 or the Winchester, which is widely considered to be the forerunner of the modern hard drive.

A hard disk drive stores information magnetically, similar to the method used to record on tape. Magnetic storage allows the disk to hold information even when the machine is powered down, and the disk format allows the information to be accessed immediately, without spooling through long reels of tape. Platters spin thousands of revolutions per minute, passing under the head on the arm, which can read, write, change or delete information.

With advantages such as speed, permanence and volume, most computers store operating systems and essential software on the hard drive. Most computer users store the majority of their files on a hard drive as well. Since computers were first introduced into the home and office, hard drive capacity has made huge advances, allowing larger files and more complex programs to be used.

Another advantage of the hard drive over its forerunners is durability. Tape can become worn with use, and a single fold could make a punch card useless. Hard drives are much more reliable, primarily because the head never touches the recording surface. The head is able to read and write while being held just over the disk, reducing the risk of scratching or general wear. Sealing the hard drive further reduces the risk of wear by keeping dust away from the sensitive platters.

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