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Glossary 367
U
UMA — unified memory allocation — System memory dynamically allocated to video.
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 find the operating system. If the computer is infected, the boot virus may replicate itself onto all
the floppy disks that are read or written in that computer until the virus is eradicated.
V — volt — The measurement of electric potential or electromotive force. One V appears across a resistance of 1 ohm
when a current of 1 ampere flows through that resistance.
W
W — watt — The measurement of electrical power. One W is 1 ampere of current flowing at 1 volt.