Specifications
Glossary
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PUN (physical unit number) A term used to
describe a device attached directly to the SCSI bus.
Also known as a SCSI ID. As many as eight SCSI
devices can be attached to a single SCSI bus, and
each must have a unique PUN or ID assigned from
7 to 0. Normally, the SCSI host adapter is assigned
the highest-priority ID, which is 7. A bootable hard
disk is assigned an ID of 0, and other nonbootable
drives are assigned higher priorities.
QAM (quadrature amplitude modulation)
A modulation technique used by high-speed
modems that combines both phase and amplitude
modulation. This technique enables multiple bits to
be encoded in a single time interval.
QDR (quad data rate) A high-speed SDRAM
technology (www.qdrsram.com) that uses separate
input and output ports with a DDR interface to
enable four pieces of data to be processed at the
same time. See also DDR.
QIC (Quarter-Inch Committee) An industry
association that sets hardware and software stan-
dards for tape-backup units that use quarter-inch-
wide tapes. QIC, QIC-Wide, Travan, and Travan NS
drives are all based on QIC standards.
Quantum Formerly a major maker of hard disk
drives and now a major maker of attached network
storage devices. Quantum-brand disk drives are
now sold and supported by Maxtor.
QuickTime An audio/video system and media
player developed by Apple Computer.
QWERTY keyboard The standard typewriter or
computer keyboard, with the characters Q, W, E, R,
T, and Y on the top row of alpha keys. Because of
the haphazard placement of characters, this key-
board can hinder fast typing.
RAID (redundant array of independent or
inexpensive disks) A storage unit that employs
two or more drives in combination for fault toler-
ance and greater performance, used mostly in file
server applications. Originally used only with SCSI
drives and host adapters, many motherboards now
feature ATA/IDE or SATA RAID implementations.
RAID On Motherboard (ROMB) A RAID con-
troller built into a motherboard.
rail A voltage tap or source inside of a power
supply. Also a plastic or metal bracket attached to
the sides of drives mounted in PCs. They fit into
channels in the side of each disk drive bay position
and might be held in position with screws or snap
into place.
RAM (random-access memory) All memory
accessible at any instant (randomly) by a micro-
processor.
RAM disk A “phantom disk drive” in which a
section of system memory (RAM) is set aside to
hold data, just as though it were a number of disk
sectors. To an operating system, a RAM disk looks
and functions like any other drive.
RAMBUS Dynamic RAM See RDRAM.
RAMDAC (random-access memory digital-to-
analog converter) A special type of DAC found
on video cards. RAMDACs use a trio of DACs—one
each for red, green, and yellow—to convert image
data into a picture. RAMDACs were formerly sepa-
rate chips but are now integrated into the 3D accel-
erator chips on most recent video cards.
random-access file A file in which all data ele-
ments (or records) are of equal length and written
in the file end to end, without delimiting charac-
ters between. Any element (or record) in the file
can be found directly by calculating the record’s
offset in the file.
random-access memory See RAM.
raster A pattern of horizontal scanning lines
normally on a computer monitor. An electromag-
netic field causes the beam of the monitor’s tube to
illuminate the correct dots to produce the required
characters.
raster graphics A technique for representing a
picture image as a matrix of dots. It is the digital
counterpart of the analog method used in TV.
Several raster graphics standards exist, including
PCX, TIFF, BMP, JPEG, and GIF.
RCA jack Also called a phono connector, this is a
plug and socket for a two-wire coaxial cable used to
connect audio and video components. The plug is
a 1/8"-thick prong that sticks out 5/16" from the
middle of a cylinder.
Appendix A
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