disk drive

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disk drive

Computing the controller and mechanism for reading and writing data on computer disks
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

disk drive

[′disk ‚drīv]
(computer science)
The physical unit that holds, spins, reads, and writes the magnetic disks. Also known as disk unit.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

disk drive

(hardware, storage)
(Or "hard disk drive", "hard drive", "floppy disk drive", "floppy drive") A peripheral device that reads and writes hard disks or floppy disks. The drive contains a motor to rotate the disk at a constant rate and one or more read/write heads which are positioned over the desired track by a servo mechanism. It also contains the electronics to amplify the signals from the heads to normal digital logic levels and vice versa.

In order for a disk drive to start to read or write a given location a read/write head must be positioned radially over the right track and rotationally over the start of the right sector.

Radial motion is known as "seeking" and it is this which causes most of the intermittent noise heard during disk activity. There is usually one head for each disk surface and all heads move together. The set of locations which are accessible with the heads in a given radial position are known as a "cylinder". The "seek time" is the time taken to seek to a different cylinder.

The disk is constantly rotating (except for some floppy disk drives where the motor is switched off between accesses to reduce wear and power consumption) so positioning the heads over the right sector is simply a matter of waiting until it arrives under the head. With a single set of heads this "rotational latency" will be on average half a revolution but some big drives have multiple sets of heads spaced at equal angles around the disk.

If seeking and rotation are independent, access time is seek time + rotational latency. When accessing multiple tracks sequentially, data is sometimes arranged so that by the time the seek from one track to the next has finished, the disk has rotated just enough to begin accessing the next track.

See also sector interleave.

The disks may be removable disks; floppy disks always are, removable hard disks were common on mainframes and minicomputers but less so on microcomputers until the mid 1990s(?) with products like the Zip Drive.

A CD-ROM drive is not usually referred to as a disk drive.

Two common interfaces for disk drives (and other devices) are SCSI and IDE. ST-506 used to be common in microcomputers (in the 1980s?).
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

disk drive

A storage device that holds, spins, reads and writes magnetic disks or optical discs (CD, DVD, MO, UDO). In this encyclopedia, disk ("k") refers to a magnetic disk drive, and disc ("c") means an optical drive. Magnetic disk drives contain non-removable platters; however, optical drives are receptacles for removable discs or cartridges. See magnetic disk, CD, DVD, magneto-optic disk and UDO.


The Early 1990s
This RAID II prototype in 1992, which embodied the principles of high performance and fault tolerance, was built by University of Berkeley graduate students. Housing 36 320MB disk drives, its total storage was less than the single drive in the cheapest PC only six years later. (Image courtesy of The Computer History Museum, www.computerhistory.org) See RAID.
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References in periodicals archive ?
However, there are many who believe the fight for dominance will eventually fade, and the most popular devices will be the ones which combine the best elements of both flash memory and disk drives. It is estimated that all of the globe's digital content takes up an incredible 2.7 zettabytes, and the figure is only growing.
Not including charges related to the acquisition of Samsung's hard disk drive business that are not yet determinable, Seagate expects gross margin as a percentage of revenue to be at least 30.5%, operating expenses (product development, marketing and administrative) to be approximately USD390m and diluted outstanding shares to be 440 million.
Following an in-depth investigation, the European Commission approved, on 19 October, the acquisition of the hard disk drive (HDD) business of Samsung Electronics of South Korea by Seagate Technology of the US.
The MHV2200BT also features a hardware accelerator that maximizes Native Command Queuing (NCQ) performance, an important feature that enables the hard disk drive controller to intelligently and simultaneously queue and reorder up to 32 instructions, resulting in a significant improvement in overall hard disk drive performance.
Nearline disk drives: These are disk drives specifically designed for backups and archives, and are unlike online storage, which requires high transaction performance.
John Fox, product marketing manager for IBM's hard disk drive range, said: "Customers wouldn't dream of not specifying the latest processor and graphic cards for their PCs, but they often forget about the hard disk drive, even though it is difficult to upgrade if needed.
The computer had a screen with 320 by 200 resolution, I believe, no hard disk drive (I added one later), 128 K of RAM, and a 14 inch color monitor.
"This merger puts us in a great position to capitalize on a very experienced management team and a rapidly growing disk drive market," said Jack Tramiel, chairman of Atari.
(Cherokee) has announced the availability of a rewritable 3.5" optical disk drive subsystem for personal computers.
The next addition is usually more storage, by means of either internal or external disk drives. Adding a 20-meg or 40-meg drive boosts weight only a pound or two but eliminates the need to switch among floppy disks containing data and programs and allows manipulation of very large data files.
SAS and SATA solutions have been in development laboratories long enough now so that we have a good under standing of the actual capability of the interfaces and disk drives in a variety of storage configurations.