Specifications
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Appendix A Glossary
dialup adapter In Windows, a software pro-
gram that uses a modem to emulate a network
interface card for networking. Most commonly
used to connect to an Internet service provider or a
dialup server for remote access to a LAN.
die An individual chip (processor, RAM, or other
integrated circuit) cut from a finished silicon chip
wafer and built into the physical package that con-
nects it to the rest of the PC or a circuit board.
differential An electrical signaling method in
which a pair of lines are used for each signal in
“push-pull” fashion. In most cases, differential sig-
nals are balanced so that the same current flows on
each line in opposite directions. This is unlike sin-
gle-ended signals, which use only one line per sig-
nal referenced to a single ground. Differential
signals have a large tolerance for common-mode
noise and little crosstalk when used with twisted-
pair wires even in long cables. Differential signaling
is expensive because two pins are required for
each signal.
digital camera A type of camera that uses a
sensor and internal or removable flash memory in
place of film to record still images. Digital cameras’
picture quality is usually rated in megapixels. See
also megapixel.
digital loopback A test that checks the
modem’s RS-232 interface and the cable that con-
nects the terminal or computer and the modem.
The modem receives data (in the form of digital sig-
nals) from the computer or terminal and immedi-
ately returns the data to the screen for verification.
digital noise reduction (DNR) Reduces audio
or video noise by the application of an algorithm
on digital audio or video data.
digital signals Discrete, uniform signals. In this
book, the term refers to the binary digits 0 and 1.
digital signature An electronic identifier used
to authenticate a message or the contents of a file.
Windows 98 and above are designed to prefer digi-
tally signed device drivers (drivers approved by the
Windows Hardware Quality Labs) and will warn
you if you try to install an unsigned device driver.
digital-to-analog converter (DAC) A device
for converting digital signals to analog signals.
VGA-based displays are analog, so video cards that
connect to them include a DAC to convert the sig-
nals to analog to drive the display.
digital video recorder (DVR) A video recorder
(TiVo, for example) that stores the recording in a
digital format, often used for time-shifting digital
television programs.
digitize To transform an analog wave to a digital
signal a computer can store. Conversion to digital
data and back is performed by a D/A converter
(DAC), often a single-chip device. How closely a
digitized sample represents an analog wave depends
on the number of times the amplitude of a wave is
measured and recorded (the rate of digitization), as
well as the number of levels that can be specified at
each instance. The number of possible signal levels
is dictated by the resolution in bits.
DIMM (dual inline memory module) A
series of memory modules used in Pentium and
newer PCs. They are available in many different
versions, including those with SDRAM, DDR or
DDR2, 3.3V, 2.5V or 1.8V, buffered, unbuffered or
registered, and in 64-bit (non-ECC/parity) or 72-bit
(ECC/parity) form. See also DDR, DDR2, and
SDRAM.
DIP (dual inline package) A family of rectan-
gular, integrated-circuit flat packages that have
leads on the two longer sides. Package material is
plastic or ceramic.
DIP switch A tiny switch (or group of switches)
on a circuit board. Named for the form factor of
the carrier device in which the switch is housed.
Direct Media Interface (DMI) A 2GBps high-
speed bus used by Intel in its E7xxx server and 9xx
desktop chipsets. Also known as Integrated Hub
Architecture (IHA) 2.0.
direct memory access (DMA) A process by
which data moves between a disk drive (or other
device) and system memory without direct control
of the central processing unit, thus freeing it up for
other tasks.
Direct Rambus DRAM See RDRAM.
directory An area of a disk that stores the titles
given to the files saved on the disk and serves as a
table of contents for those files. Contains data that
identifies the name of a file, the size, the attributes
(system, hidden, read-only, and so on), the date
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