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`A Dictionary of
`Computer
`Science
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`A Dictionary of
`
`Computer
`Science
`
`SEVENTH EDITION
`
`NOV O 6 2017
`
`OXFORD
`
`UNIVERSITY PRESS
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`OXFORD
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`disk pack
`
`166
`
`cell and the maximum is two cells. For the
`same spacing of flux transitions the MFM
`method allows twice as many bits to be
`encoded in a unit distance; it is thus some(cid:173)
`times referred to as a double-density
`recording.
`Modified modified frequency modulation
`(M2FM) is a modified form of MFM that
`deletes flux transitions between two Os if they
`are followed by a 1.
`Optical disk formats are broadly similar to
`those of magnetic disk, except that the tracks
`usually take the form of a continuous spiral
`and the path of this is often determined by a
`groove pressed into the disk surface during
`manufacture (see also CD-ROM FORMAT
`STANDARDS).
`See also FORMATTER.
`
`disk pack One form of *exchangeable disk
`store, now obsolete, that consisted of an
`assembly of identical 14" diameter rigid
`*magnetic disks mounted coaxially and
`equally spaced. Storage capacities ranged
`from 30 to 300 megabytes. Disk packs were
`introduced by IBM in 1963.
`
`*LCDs (liquid-crystal displays), *plasma
`panels, and *electroluminescent
`displays. 2. A method of presenting graph(cid:173)
`ical or pictorial images. See also RASTER(cid:173)
`SCAN DISPLAY, VECTOR DISPLAY. 3. To make
`information visible in a temporary form.
`
`Display Port A *standard interface issued
`by *VESA in 2006 for connecting a video
`source to a display device; as such, it sup(cid:173)
`plants the older *VGA and *DVI standards.
`Unlike its predecessors, it transmits data in
`the form of *packets. A variant with a smaller
`connector called Mini DisplayPort (MDP)
`was released by Apple in 2008. See also
`THUNDERBOLT.
`
`display processor A specialized *I/0
`processor used to mediate between a file of
`information that is to be displayed and a
`display device. It reformats the information
`as required and provides the information in
`accordance with the timing requirements of
`the display system. In most modem personal
`computers this function is carried out by a
`special *graphics processing unit.
`
`disk stack See FIXED DISK DRIVE.
`
`disk striping See RAID, STRIPE DISK.
`
`disk-to-plate See DTP.
`
`disk unit Another name for disk drive.
`
`dispatcher Another name for low-level
`scheduler. See SCHEDULER.
`
`dispersion See MEASURES OF VARIATION.
`
`displacement mapping A method of
`approximating a bumpy surface by offsetting
`the base surface by the appropriate bump
`height and then rendering the surface. It
`gives' a more realistic rendering than *bump
`mapping but is more expensive to perform.
`
`display 1. A device that can be attached to a
`computer in order to present transient
`images-textual or pictorial-on its screen
`(see TEXT MODE, GRAPHICS MODE). For many
`years the most widely used display device
`was the *cathode-ray tube with colour spe(cid:173)
`cified by RGB signals. Other display tech(cid:173)
`nologies use *flat-panel displays, which in
`recent years have largely replaced cathode(cid:173)
`ray tubes as prices have fallen. These include
`
`Distiller Short for Adobe Acrobat Distiller.
`See ACROBAT.
`
`distributed array processor See ARRAY
`PROCESSOR.
`
`distributed artificial intelligence
`(DAI) An approach to *artificial intelligence
`in which processing takes place not in a
`single algorithm but is distributed across a
`number of agents, possibly many. Each
`agent is autonomous, with its own actions
`and belief space, and the behaviour of the
`whole system, which may or may not solve a
`particular problem, is characterized by its
`emergent properties.
`
`distributed computing environment
`SeeDCE.
`
`Distributed Concurrent Versions
`System See DCVS.
`
`distributed database A *database in
`which the data is contained within a number
`of separate subsystems, usually in different
`physical locations. If the constituent subsys(cid:173)
`tems are essentially similar, the system is
`said to be homogeneous, otherwise it is
`said to be heterogeneous. Distributed
`
`Ex. 2014-0004
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`

`467
`
`requirements specification phase
`
`execution and return of any results from the
`processor executing the procedure body to
`that executing the procedure call.
`These factors have given rise to-a number
`of different proposals for the course of action
`to be followed in the event of one or other of
`the systems failing; essentially to have the
`procedure body executed either at least once
`(by *retry) or at most once. These proposals
`tend to reflect the different priorities
`attached to the effect on the total system in
`the event of part of it failing.
`
`remote sensing The technique whereby
`sensors located remotely from a computer
`are used to produce inputs for a digital sys(cid:173)
`tem. These inputs are then transmitted
`either by wire or radio techniques to the
`computer. An example is the use of digital
`thermometers and humidity detectors in
`large buildings: the sensors transmit their
`readings to a central computer that opti(cid:173)
`mizes energy use by regulating heat and air
`conditioning. Recent developments enable
`wireless sensors to connect with each other
`to form *wireless sensor networks.
`
`rendering The part of computer graphics
`that is concerned with getting from a three(cid:173)
`dimensional scene (possibly containing
`moving objects) to a picture or animated
`sequence, with more or less sophistication in
`terms of the effect achieved.
`
`rendezvous A method of synchronizing
`concurrent tasks in * Ada.
`
`repair time The (sometimes average) time
`required to diagnose and repair a computer
`failure, either hardware or software. In
`combination with MTBF (mean time
`between failures) the MTTR (mean time to
`repair) provides a figure-of-merit for system
`*reliability and/ or *uptime.
`
`repeated measures In statistical analysis
`of data, successive observations obtained
`from the same source (such as an instru(cid:173)
`ment, operator, animal, etc.). Theoretical
`models must take account of the *correl(cid:173)
`ations between the successive observations.
`In some circumstances the changes between
`successive observations may be regarded as
`statistically independent.
`
`repeater In general, a device that amplifies
`a signal to allow it to transmit over greater
`distances than might otherwise be possible.
`For free-space signalling systems in which
`the signal is presented as a modulated car(cid:173)
`rier, the repeater may also move the signal to
`a different carrier frequency.
`
`repeat-until loop See DO-WHILE LOOP.
`
`repertoire Short for instruction repertoire.
`See INSTRUCTION SET.
`
`repetition codes A trivial family of *cyclic
`*perfect *error-correcting *block codes, in
`which the codewords are formed merely by
`repeating the message words r times. Con(cid:173)
`sidered as (n, k) codes (see BLOCK CODE),
`these codes have n = rk for some k.
`
`repo Short for repository, especially one
`used for storing *source code.
`
`report generator See GENERATOR, RPG.
`
`repository (repo) A location in which
`important data, such as program code, are
`stored.
`
`representation Storage and *data values
`used to carry information.
`
`request for comments See RFC.
`
`request input Input in computer graphics
`that is initiated by the application. The
`application waits until the input is entered by
`the operator before resuming.
`
`requirements analysis The analysis that
`is necessary for the production of an
`*expression of requirements, or a *user, a
`*software, or a *system requirements
`specification.
`
`requirements specification See
`SOFTWARE REQ(!IREMENTS SPECIFICATION,
`SYSTEM REQUIREMENTS SPECIFICATION, USER
`REQUIREMENTS SPECIFICATION.
`
`requirements specification phase The
`phase in the *software or *system life cycle
`where the *user, *software, or *system
`requirements specification is produced. The
`phase activities include elicitation, capture,
`*expression, and *review of requirements.
`
`Ex. 2014-0005
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