GLOSSARY
central processing unit (CPU)
The heart of the computer system that executes programmed instructions. It includes the arithmetic logic unit (ALU) for performing all math and logic operations, a control section for interpreting and executing instructions, internal memory for temporary storage of program variables and other functions.
channel
A collection of electronic circuits used in the process of writing and reading information to and from magnetic media.
character
An ordered collection of bits representing one of a set of predefined symbols. Often the term is used interchangeably with byte, but this is inexact.
closed loop
A control technique that enables the positioning system to correct
closed loop servo
A servo control technique that uses position feedback to correct
cluster
The smallest allocatable unit of disk storage allowed by
controller
An electronic device for connecting one or more mass storage peripherals (rigid disk drives, tape drives, and optical disk drives) to the input/output circuits of a host computer. Controllers vary in complexity, with more sophisticated units able to buffer and schedule commands, correct data errors, and bypass media defects without host intervention.
controller
A miniature CPU dedicated to controlling a peripheral device, such as a disk drive, tape drive, video display terminal, or printer. The controller executes commands from the central processing unit and reissues commands to the peripheral device.
correctable error
An error that can be overcome by the use of Error Detection and Correction.
cylinder
On several disk surfaces sharing a common rotational axis, the aggregate of tracks at a given radial position. A set of disk tracks that are simultaneously under the set of read/write heads. This
cylinder zero
The outermost cylinder in a drive that can be used for data storage.
D
data
An ordered collection of information. In a specific case, it is the information processed by a computer.
data separator
An electronic circuit which decodes playback data and produces separate clock and data bits. Sometimes incorrectly used to denote data synchronizer.
data synchronizer
An electronic circuit producing a clock signal that is synchronous with the incoming data stream. This clock signal is then used to decode the recording code being used into user data.
data transfer rate
In a disk or tape drive, the rate at which data is transferred to or from the storage media. It is usually given in thousands of bits per second (Kbit/second) or millions of bits per second (Mbit/second).
dedicated landing zone
A designated radial zone on the disk where contact starting and stopping occur by design.
dedicated servo
A servo scheme in which a prerecorded pattern on an otherwise unused disk surface provides position information to the servo circuitry by means of a head reading that surface.
defect
A magnetic imperfection in a recording surface.
defect management
A general methodology of avoiding data errors on a recording surface by avoiding the use of known bad areas of media. Usually defective sectors or tracks are retired and data are written in alternate locations. Several algorithms are possible such as “sector slipping,” or “spare sector per track.”
defect map
A list of defects that fall within a pass/fail criteria of a user. This list is usually used by an operating system or a disk drive controller for defect management.
defect skipping
A defect management scheme for avoiding surface defects. It has data written before and after the defect, instead of using alternate tracks or sectors to avoid use of the defective area.
density
Generally, recording density. See areal, bit, and storage density.
DC erase
The method of erasing a track using a DC write/erase current through either a Read/Write or Erase head.
digital
Any system that processes digital binary signals (having only values of a 1 or 0; usually in bits and bytes) rather than analog signals (signals that can have many values)
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