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Hard Disk Drive

A hard disk drive (HDD; also hard drive, hard disk, or disk drive) is a device for storing and retrieving digital information, primarily computer data. It consists of one or more rigid (hence "hard") rapidly rotating discs (often referred to as platters), coated with magnetic material and with magnetic heads arranged to write data to the surfaces and read it from them.

Hard drives are classified as non-volatile, random access, digital, magnetic, data storage devices. Introduced by IBM in 1956, hard disk drives have decreased in cost and physical size over the years while dramatically increasing in capacity and speed.

Hard disk drives have been the dominant device for secondary storage of data in general purpose computers since the early 1960s. They have maintained this position because advances in their recording capacity, cost, reliability, and speed have kept pace with the requirements for secondary storage.

External removable hard disk drives offer independence from system integration, establishing communication via connectivity options, such as USB.  Plug and play drive functionality offers system compatibility, and features large volume data storage options, but maintains a portable design.

  • The HDD installs in one of the 3-1/2 inch internal drive bays in the PC. It is secured by machine screws.

  • It is powered by a 4 conductor cable coming from the power supply.

  • Data to and from the motherboard is carried on a 40-pin IDE (Integrated Drive Electronics) cable.

  • Data is stored magnetically on multiple rigid disks that are stacked up like pancakes. Small arms with magnetic pickups move rapidly back and forth across the top and bottom surface of each disk in the drive. The sensors float just a few microns above the rotating disk surface and can read and write data at very high rates.

  • Most commercially available hard drives rotate at 5400 or 7200 RPM (revolutions per minute) which translates to 90 or 120 revolutions per second respectively. The data transfer rate from the drive to the motherboard is 33 Mbytes/second in bursts. Newer drives are capable of higher speeds up to 66 Mbytes/sec. To use this faster drive, the PC must have an ATA/66 interface that is capable of keeping up with it.

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