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Glossary 211
UPS — uninterruptible power supply — A backup power source used when the electrical
power fails or drops to an unacceptable voltage level. A UPS keeps a computer running
for a limited amount of time when there is no electrical power. UPS systems typically
provide surge suppression and may also provide voltage regulation. Small UPS systems
provide battery power for a few minutes to enable you to shut down your computer.
USB — universal serial bus — A hardware interface for a low-speed device such as a
USB-compatible keyboard, mouse, joystick, scanner, set of speakers, printer, broadband
devices (DSL and cable modems), imaging devices, or storage devices. Devices are
plugged directly in to a 4-pin socket on your computer or in to a multi-port hub that plugs
in to your computer. USB devices can be connected and disconnected while the computer
is turned on, and they can also be daisy-chained together.
UTP — unshielded twisted pair — Describes a type of cable used in most telephone
networks and some computer networks. Pairs of unshielded wires are twisted to protect
against electromagnetic interference, rather than relying on a metal sheath around each
pair of wires to protect against interference.
UXGA — ultra extended graphics array — A video standard for video cards and
controllers that supports resolutions up to 1600 x 1200.
V
video controller — The circuitry on a video card or on the system board (in computers
with an integrated video controller) that provides the video capabilities—in combination
with the monitor—for your computer.
video memory — Memory that consists of memory chips dedicated to video functions.
Video memory is usually faster than system memory. The amount of video memory
installed primarily influences the number of colors that a program can display.
video mode — A mode that describes how text and graphics are displayed on a monitor.
Graphics-based software, such as Windows operating systems, displays in video modes
that can be defined as x horizontal pixels by y vertical pixels by z colors. Character-based
software, such as text editors, displays in video modes that can be defined as x columns
by y rows of characters.
video resolution — See resolution.
virus — A program that is designed to inconvenience you or to destroy data stored on
your computer. A virus program moves from one computer to another through an
infected disk, software downloaded from the Internet, or e-mail attachments. When an
infected program starts, its embedded virus also starts.
A common type of virus is a boot virus, which is stored in the boot sectors of a floppy
disk. If the floppy disk is left in the drive when the computer is shut down and then turned
on, the computer is infected when it reads the boot sectors of the floppy disk expecting to