Glossary 15

system board
The main printed circuit board inside the system unit into which other boards and
major chip components, such as the system microprocessor, are connected.
T
tpi
Tracks per inch.
track
Any of many concentric circular regions on a disk for storing data. Tracks are
divided into s ectors. One mea sure of stor a ge density of a dis k is tpi.
U
Ultra DMA
A protocol developed by Quantum Corporation and Intel that supports burst mode
data transfer rates of 33. 3 M Bps. This is twic e a s fast as the pr evious disk dri ve
standard for PCs, and is n e c essary to t a ke advantag e of new, fast er Ultra ATA di s k
drives. The of ficial name f or the protoc o l is Ultra DM A/ 33.
USB
Universal Serial Bus. An external bus standard that supports data transfer rates of
12 Mbps (12 million bits per second). A single USB port can be used to connect up
to 127 peripheral devices, such as mice, modems, and keyboards. USB also
supports Plug-and-Play installation and hot plugging. It is expected to eventually
replace serial and parallel ports.
V
VESA
Video Electr onics Sta ndards Associ a tion. The sou rce of a Sup er VGA standar d used
on many video boards.
virus
Software tha t copies itse lf onto hard dr ives and disket tes without u ser intervent ion,
usually when a diskette is placed into the drive of a computer. Viruses usually
trigger a harmless or destructive occurrence on the system, activated by some preset
condition. Viruses are frequently written with antisocial intent.
VGA
Video Graphics Array. Graphics technology that supports up to 256 K colors and a
graphics resolution of 640 by 480 pixels.
volatile memory
Storage media that loses its data when system power is turned off. Standard
memory and memory added to the system are volatile memory. See nonvolatile
memory.