Specifications

Glossary
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DEBUG The name of a utility program included
with DOS and used for specialized purposes, such
as altering memory locations, tracing program exe-
cution, patching programs and disk sectors, and
performing other low-level tasks.
decibel (dB) A logarithmic measure of the ratio
between two powers, voltages, currents, sound
intensities, and so on. Signal-to-noise ratios are
expressed in decibels.
dedicated line A user-installed telephone line
that connects a specified number of computers or
terminals within a limited area, such as a single
building. The line is a cable rather than a public-
access telephone line. The communications chan-
nel also can be referred to as nonswitched because
calls do not go through telephone company switch-
ing equipment.
dedicated servo surface In voice-coil-actuated
hard disk drives, this is one side of one platter
given over to servo data that is used to guide and
position the read/write heads.
default Any setting assumed at startup or reset
by the computer’s software and attached devices
that is operational until changed by the user. An
assumption the computer makes when no other
parameters are specified. When you type
DIR with-
out specifying the drive to search, for example, the
computer assumes you want it to search the default
drive. The term default is used in software to
describe any action the computer or program takes
on its own with embedded values.
defect map A list of unusable sectors and tracks
coded onto a drive during the low-level format
process.
defragmentation The process of rearranging
disk sectors so files are stored on consecutive sec-
tors in adjacent tracks.
degauss 1) To remove magnetic charges or to
erase magnetic images. Normal applications include
CRT monitors and disks or tapes. Most monitors
incorporate a degaussing coil, which surrounds the
CRT, and automatically energize this coil for a few
seconds when powered up to remove color or
image-distorting magnetic fields from the metal
mask inside the tube. Some monitors include a but-
ton or control that can be used for additional appli-
cations of this coil to remove more stubborn
magnetic traces. 2) The act of erasing or demagne-
tizing a magnetic disk or tape using a special tool
called a degaussing coil.
density The amount of data that can be packed
into a certain area on a specific storage media.
desktop A personal computer that sits on a desk.
device driver Originally, a memory-resident
program loaded by
CONFIG.SYS that controls an
unusual device, such as an expanded memory
board. Windows also uses device drivers, but they
are loaded through the Windows Registry or
.INI files.
DHCP (Dynamic Host Configuration
Protocol) A protocol for assigning dynamic IP
addresses to devices on a network. With dynamic
addressing, a device can have a different IP address
every time it connects to the network. Routers,
gateways, and broadband modems can function as
DHCP hosts to provide IP addresses to other com-
puters and devices on the network.
Dhrystone A benchmark program used as a
standard figure of merit indicating aspects of a
computer system’s performance in areas other than
floating-point math performance. Because the pro-
gram does not use any floating-point operations,
performs no I/O, and makes no operating system
calls, it is most useful for measuring the processor
performance of a system. The original Dhrystone
program was developed in 1984 and was written in
Ada, although the C and Pascal versions became
more popular by 1989.
DHTML (Dynamic HTML) A collective term
for cascading style sheets, layering, dynamic fonts,
and other features encompassed in standard HTML
4.0, Netscape Navigator 4.x and above, and
Internet Explorer 4.x and above. Because of differ-
ences in how browsers interpret particular DHTML
features, many developers incorporate browser-
checking code into their web pages to enable or
disable certain features depending on the browser
being used to view the page.
diagnostics Programs used to check the opera-
tion of a computer system. These programs enable
the operator to check the entire system for any
problems and indicate in which area the
problems lie.
Appendix A
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