Specifications

Glossary
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Ultra DMA (UDMA or Ultra ATA) A protocol
for transferring data to an ATA interface hard drive.
The Ultra DMA/33 protocol transfers data in burst
mode at a rate of 33MBps, whereas the even faster
Ultra DMA/66 protocol transfers at 66MBps.
Ultra DMA/66 also requires the use of a special
80-conductor cable for signal integrity. This cable
also is recommended for Ultra DMA/33 and is back-
ward compatible with standard ATA/IDE cables. The
fastest UDMA modes are Ultra DMA/100 (supported
by most recent chipsets) and Ultra DMA/133 (intro-
duced in 2001).
Ultra High Frequency (UHF) The frequency
band between 300 and 3,000MHz.
UltraXGA (UXGA) A screen resolution of
1,600×1,200.
Ultrium The high-capacity implementation of
the Linear Tape Open (LTO) standard. LTO-3
Ultrium is the highest-capacity version currently
available, with native/2:1 compressed capacity of
400/800GB.
UMB (upper memory block) A block of
unused memory in the upper memory area (UMA),
which is the 384KB region between 640KB and
1MB of memory space in the PC. BIOS chips and
memory buffers on add-on cards must be config-
ured to use empty areas of the UMB; otherwise,
they will not work.
unformatted capacity The total number of
bytes of data that can fit on a disk. The formatted
capacity is lower because space is lost defining the
boundaries between sectors. For example, some
vendors have referred to the high-density 1.44MB
floppy disk as a 2.0MB disk (2.0MB is the unformat-
ted capacity). However, because most media is pre-
formatted today, this issue is fading away.
Unicode A worldwide standard for displaying,
interchanging, and processing all types of language
texts, including both those based on letters (such as
Western European languages) and pictographs
(such as Chinese, Japanese, and Korean).
uninterruptible power supply (UPS) A
device that supplies power to the computer from
batteries so power will not stop, even momentarily,
during a power outage. The batteries are recharged
constantly from a wall socket.
Universal Asynchronous Receiver
Transmitter See UART.
unzipping The process of extracting one or
more files from a PKZIP or WinZip-compatible
archive file.
UPC (universal product code) A 10-digit
computer-readable bar code used in labeling retail
products. The code in the form of vertical bars
includes a five-digit manufacturer identification
number and a five-digit product code number.
update To modify information already contained
in a file or program with current information.
UPnP (universal plug and play) A distrib-
uted, open networking architecture standard cre-
ated by the UpnP forum (www.upnp.org) that
leverages TCP/IP to enable seamless peer-to-peer
networking in addition to control and data transfer
among networked devices in the home and office.
upper memory area (UMA) The 384KB of
memory between 640KB and 1MB. See also UMB.
URL (uniform resource locator) The primary
naming scheme used to identify a particular site or
file on the World Wide Web. URLs combine infor-
mation about the protocol being used, the address
of the site where the resource is located, the subdi-
rectory location at the site, and the name of the
particular file (or page) in question.
USB (universal serial bus) USB version 1.1 is a
12Mbps (1.5MBps) interface over a simple four-wire
connection. The bus supports up to 127 devices
and uses a tiered star topology built on expansion
hubs that can reside in the PC, any USB peripheral,
or even standalone hub boxes. USB 2.0, also called
High-Speed USB, runs at 480Mbps and handles
multiple devices better than USB 1.1.
utility A program that carries out routine proce-
dures to make computer use easier.
UTP (unshielded twisted pair) A type of wire
often used indoors to connect telephones or com-
puter devices. Comes with two or four wires twisted
inside a flexible plastic sheath or conduit and uses
modular plugs and phone jacks.
V.21 An ITU standard for modem communica-
tions at 300bps. Modems made in the U.S. or
Canada follow the Bell 103 standard but can be set
Appendix A
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