|
This500 word Glossary cover all the major peripherals of computer,i/o
devices,Networking and Tele Communication
A
adapter Also known as an add-on card, controller, expansion card, or I/O card. Adapters are installed
in
expansion slots to enhance the processing power of the computer or to communicate with other devices.
Examples of adapters include asynchronous communication, floppy disk-controller, and expanded
memory.
address A unique memory location permitting reading or writing of data to/from that location.
Network
interface cards and CPUs often use shared addresses in RAM to move data between programs.
analog-to-digital converter (ADC) A device that converts analog input signals to digital output
signals used
to represent the amplitude of the original signal.
application software A computer program designed to help people perform a certain type of work.
An
application can manipulate text, numbers, graphics, or a combination of elements. Some application packages
focus on a single task and offer greater computer power while others, called integrated software, offer
less
power but include several applications, such as word processing, spreadsheet, and database programs.
An
application may also be referred to as software, program, instructions, or task. See also software
areal density The amount of data that can be stored in one area of a disk-hard or floppy.
ASCII (American Standard Code for Information Interchange) The data alphabet used in the IBM
PC to
determine the composition of the 7-bit string of 0s and 1s that represents each character (alphabetic,
numeric,
or special). It is a standard way to transmit characters.
asynchronous communication (ASYNC) A type of serial communication by which data is passed between
devices. "Asynchronous" means that the timing of each character transmitted is independent
of other
characters.
average access time The time (in milliseconds) that a disk drive takes to find the right track
in response to a
request (the seek time), plus the time it takes to get to the right place on the track (the latency).
B
back up To make a copy of a file, group of files, or the entire contents of a hard disk.
baud rate A measure of the actual rate of symbols transmitted per second, which may represent
more than
one bit. A given baud rate may have more than one bps (bits per second) rate. Baud rate is often used
interchangeably with bps, although this is technically incorrect.
binary A numbering system with two digits, 0 and 1, used by computers to store and process information.
BIOS (basic input/output system) A collection of primitive computer routines (stored in ROM
in a PC) that
control peripherals such as the video display, disk drives, and keyboard.
bisynchronous (BISNYC) Computer communications in which both sides simultaneously transmit and
receive data.
bit A binary digit: the smallest piece of information that can be recognized and processed by
a computer. A
bit is either 0 or 1. Bits can form larger units of information called nibbles (4 bits), bytes (8 bits),
and words
(usually 16 bits). See also data bit
bits per second (bps) The number of data bits sent per second between two modems. Used as a
measure of
the rate at which digital information is handled, manipulated, or transmitted. Similar, but not identical,
to baud
rate.
buffer An area of RAM (usually 512 bytes plus another 16 for overhead) in which DOS stores data
temporarily. See also frame buffer
bus A group of wires used to carry a set of related signals or information within
a computer from one device to another.
byte A sequence of adjacent binary digits that the computer considers a unit. A byte consists
of 8 bits.
C
cache An amount of RAM set aside to hold data that is expected to be accessed again. The second
access,
which finds the data in RAM, is very fast. (Pronounced like "cash.")
CGA IBM's first color graphics standard, capable of 320 by 320 resolution at four colors (or
gray shades on
laptops), or 640 by 200 at two colors (black and white). CGA-only laptops are behind the times.
chip An integral part of the PC. These are very tiny, square or rectangular slivers of material
(usually silicon)
with electrical components built in. Some of the chips in a computer aid in memory, but the most important
chip is the microprocessor. This is the "8088", "286", "386", or "486"
that is referred to when talking about a
specific machine's features.
clone An IBM PC/XT- or AT-compatible computer made by another manufacturer.
cluster A hard-disk term that refers to a group of sectors, the smallest storage unit recognized
by DOS. On
most modern hard disks, four 512-byte sectors make up a cluster, and one or more clusters make up a
track.
CMOS (complementary metal oxide semiconductor) chip A type of memory chip that retains its data
when
power is turned off as long as it retains a trickle of power from a battery.
coding The act of programming a computer; specifically, generating source code in the language
of the
program's choice. The most popular languages used by programmers are Pascal, C, and C++.
COM Communications port or serial port used by modems, mice, and some printers. DOS assigns
these ports
as COM1, COM2, and sometimes COM3 and COM4. DOS also lets you refer to the first communications port
as AUX. Note: Some programs count communications ports starting with 0, so "Port 0"
or "Communications Port 0" would
be COM1, and "Port 1" would be COM2.
communications parameters Settings that define how your communications software will handle incoming
data and transmit outgoing data. Parameters include bits per second, parity, data bits, and stop
bits.
convergence A video term that describes the way in which the three beams that generate the three
color dots
(red, green, blue) should meet. When all three dots are excited at the same time and their relative
distance is
perfect, the result is pure white. Deviation from this harmony (due to an incorrect relationship of
the beams to
each other) results in poor convergence. This causes white pixels to show bits of color and can decrease
image sharpness and resolution.
CPU (central processing unit) The functional "brain" of a computer; the element that
does the actual adding
and subtracting of 0s and 1s and the manipulation and moving of data that is essential to computing.
D
database A file consisting of a number of records or tables, each of which is constructed of
fields (in column
format) of a particular type, together with a collection of operations that facilitate searching, sorting,
recombination, and similar acts.
data bits The bits sent by a modem. These bits make up characters and don't include the bits
that make up
the communications parameters. See also bit
device Any piece of computer hardware.
device-level interface An interface that uses an external controller to connect the disk drives
to the PC.
Among its other functions, the controller converts the serial stream of data read from the drive into
parallel
data for the host computer's bus. ST506 and ESDI are device-level interfaces.
digital-to-analog converter (DAC) A circuit that accepts digital input signals and converts
them to analog
output signals. Sometimes called DAC chips, they are used in VGA video cards, for example.
directory A list of file names and locations of files on a disk.
disk A circular metal platter or mylar diskette with magnetic material on both sides that stores
programs and
data. Disks are rotated continuously so that read/write heads mounted on movable or fixed arms can read
or
write programs or data to and from the disk. See also floppy disk, hard disk
disk cache A portion of a computer's RAM set aside for temporarily holding information read from
a disk.
The disk cache does not hold entire files as does a RAM disk, but information that has either been recently
requested from a disk or has previously been written to a disk.
disk defragmenter Defragmentation is the rewriting of all the parts of a file on contiguous
sectors. When
files on a hard disk drive are being updated, the information tends to be written all over the disk,
causing
delays in file retrieval. Defragmentation reverses this process, and is often achieved with special
defragmentation programs that provide up to 75 percent improvement in the speed of disk access and
retrieval.
disk drive The motor that actually rotates the disk, plus the read/write heads and associated
mechanisms,
usually in a mountable housing. Sometimes used synonymously to mean the entire disk subsystem.
disk format Refers to the method in which data is organized and stored on a floppy or hard disk.
diskette See floppy disk
DOS (disk operating system) A set of programs that control the communications between components
of
the computer. Examples of DOS functions are: displaying characters on the screen, reading and writing
to a
disk, printing, and accepting commands from the keyboard. DOS is a widely used operating system on IBM-compatible
personal computers (PCs).
dot matrix printer A type of printer technology using a print head with pins to poke out arrays
of dots that form text and graphics.
dot pitch A color monitor characteristic; specifically, the distance between the holes in the
shadow mask. It
indirectly describes how far apart the individual dots are on screen. The smaller the dot pitch, the
finer the
image's "grain." Some color monitors, such as the Sony Trinitron, use a slot mask (also known
as an aperture
grille) that is perforated by strips, not holes, in the shadow mask. In this case, the dots are arranged
in a linear
fashion, and their density is called striped dot pitch. (Monochrome monitors do not use a shadow mask
and
therefore do not have a dot pitch.)
download To receive information from another modem and computer over the telephone lines. It
is the
opposite of upload.
DRAM (dynamic random-access memory) The most commonly used type of memory, found on video boards
as well as on PC system boards. DRAM is usually slower than VRAM (video random-access memory), since
it has only a single access pathway.
drive array A storage system composed of several hard disks. Data is divided among the different
drives for
greater speed and higher reliability.
DSDD (double-sided, double-density) On PCs and laptops, DSDD means 720K 3 1/2-inch diskettes
or 360K 5
1/4-inch diskettes.
DSHD (double-sided, high-density) On PCs and laptops, DSHD means 1.44Mb 3 1/2-inch diskettes
or 1.2Mb
5 1/4-inch diskettes.
E
EISA (Extended Industry Standard Architecture) Primarily a desktop specification for high-performance
computers. Competes with IBM's Micro Channel architecture (MCA). EISA computers can use existing PC,
XT, and AT add-in cards; MCA computers can't. See also Micro Channel architecture
E-mail (electronic mail) The exchange of messages via a bulletin board or on-line service. One
user
leaves the message on the service "addressed" to another user. The other user later connects
to the same
service and can read the message and reply to it.
expanded memory Memory that can be used by some DOS software to access more than the normal
640K
(technically, more than 1Mb). 80386, 80386SX, and 80486 computers can create expanded memory readily
by
using an EMS (expanded memory specification) driver provided with DOS, through Microsoft Windows, or
through a memory manager such as Quarterdeck QEMM or Qualitas 386 To The Max. To use expanded
memory, a program must be EMS-aware or run under an environment such as Microsoft Windows. 8088- and
80286-based computers often need special hardware to run expanded memory. See also memory
extended memory Memory above 1Mb in 80286 and higher computers. Can be used for RAM disks, disk
caches, or Microsoft Windows, but requires the processor to operate in a special mode (protected mode
or
virtual real mode). With a special driver, you can use extended memory to create expanded memory. See
also
memory, RAM, ROM
F
file A collection of related records treated as a unit. In a computer system, a file can exist
on magnetic tape,
disk, or as an accumulation of information in system memory. A file can contain data, programs, or both.
floppy disk A removable, rotating, flexible magnetic storage disk. Floppy disks come in a variety
of sizes, but
3 1/2-inch and 5 1/4-inch are the most popular. Storage capacity is usually between 360K and 1.44MB.
Also
called flexible disk or diskette. See also disk, hard disk
floppy drive A disk drive designed to read and write data to a floppy disk for transfer to and
from a computer.
format A DOS command that records the physical organization of tracks and sectors on a disk.
frame buffer A large section of memory used to store an image to be displayed on-screen as well
as parts of
the image that lie outside the limits of the display. See also buffer
G
GCR (group coded recording) A hard-disk term for a storage process where bits are packaged as
groups,
with each group assigned to and stored under a particular code. Used by RLL drives.
graphics coprocessor Similar to a math coprocessor in concept, a programmable chip that can
speed video
performance by carrying out graphics processing independently of the microprocessor. Graphics
coprocessors can speed up performance in two ways: by taking over tasks the main processor would lose
time performing and by optimizing for graphics. Video adapter cards with graphics coprocessors are
expensive compared to those without them, but they speed up graphics operations considerably. Among
the
coprocessor's common abilities are drawing graphics primitives and converting vectors to bitmaps.
H
handshaking A modem term that describes the initial exchange between modems. It's like "are
you there?"
with the response "I am here."
hard disk A mass storage device that transfers data between the computer's memory and the disk
storage
media. Hard disks are nonremovable, rotating, rigid, magnetic storage disks. There are some types of
hard
disk with removable rigid media in the form of disk packs. See also disk
hardware The physical components of a computer.
head actuator In a disk drive, the mechanism that moves the read/write head radially across
the surface of the
platter of the disk drive.
high-speed modem A modem operating at speeds from 9,600 to 19,200 bits per second.
host system In telecommunications, the system that you have called up and to which you are connected,
such as a BBS (bulletin board system) or an on-line service such as CompuServe.
Hz (Hertz) A unit of measurement. This used to be called cycles per second.
IDE (integrated drive electronics) A disk drive with its own controller electronics built in
to save space and
money. Many laptops use IDE drives.
I
instructions See application software
Intel A major manufacturer of integrated circuits used in computers. Intel makes the 8086 family
of
microprocessors and its derivatives: the 8088, 80286, 80386SX and DX, and 80486SX and DX. These are
the
chips used in the IBM PC family of computers and all the computers discussed in this book.
integrated circuit (IC) A tiny complex of electronic components and their connections that is
produced in or
on a slice of material (such as silicon). A single IC can hold many electronic elements. Also called
a chip.
interlaced and noninterlaced scanning Two monitor schemes with which to paint an image on the
screen.
Interlaced scanning takes two passes, painting every other line on the first pass and filling in the
rest of the
lines on the second pass. Noninterlaced scanning paints all the lines in one pass and then paints an
entirely
new frame. Noninterlaced scanning is preferable because it reduces screen flicker, but it's more expensive.
interleaving A hard-disk term that describes a method of arranging disk sectors to compensate
for relatively
slow computers. Spreads sectors apart instead of arranging them consecutively. For example, 3:1 interleaving
means your system reads one out of every three tracks on one rotation. The time required for the extra
spin
lets the read/write head catch up with the disk drive, which might otherwise outrun the head's ability
to read
the data. Thanks to track buffering and the speed of today's PCs, interleaving is obsolete. Look for
a "1:1
interleaving," which indicates a noninterleaved drive.
I/O (input/output) Input is the data flowing into your computer. Output is the data flowing out.
I/O can refer
to the parallel and serial ports, keyboard, video display, and hard and floppy disks.
interrupt request (IRQ) A request for attention and service made to the CPU. The keyboard and
the serial
and parallel ports all have interrupts. Setting two peripherals to the same IRQ is a cause of hair pulling
among
desktop PC users; laptops don't suffer the problem as badly because they have few, if any, add-on products
that need interrupts set.
ISA (Industry Standard Architecture) Computers using the same bus structure and add-in cards
as the IBM
PC, XT, and AT. Also called classic bus. It comes in an 8-bit and 16-bit version. Most references to
ISA mean
the 16-bit version. Many machines claiming ISA compatibility will have both 8- and 16-bit connectors
on the
motherboard.
K
kilobyte (KB) 1,024 bytes. Sometimes abbreviated as k (lowercase), K-byte, K, or KB for kilobyte
and Kb for
kilobit (1,024 bits). When in doubt about whether an abbreviation refers to kilobytes or kilobits, it's
probably
kilobytes, with these exceptions: the speed of a modem (as in 2.4 kilobits per second) and the transfer
rate of
a floppy disk (as in 500 kilobits per second).
L
local area network (LAN) A small- to moderate-size network in which communications are usually
confined
to a relatively small area, such as a single building or campus.
logical drive A drive that has been created by the disk operating system (DOS). This is done
either at the
preference of the user or because the DOS version does not allow a formatted capacity in excess of 32MB.
A
user with a 100MB hard disk will want to use more than 32MB, so a program will tell DOS there are a
bunch of
"logical" drives that add up to 100MB. DOS 5.0 eliminates this need.
log on or log off The process of connecting or disconnecting your computer to another system
by modem.
M
MB See megabyte
mega One million, but with computers it typically means 1,048,576 (1,024 times 1,024).
megabyte (MB) 1,048,576 bytes (1,024 times 1,024). Used to describe the total capacity of a
hard or floppy
disk or the total amount of RAM. Sometimes abbreviated as Mb, M, MB, or meg for megabyte; and Mb, M-bit,
or Mbit for megabit. When in doubt, it's probably megabyte, not megabit, with these exceptions: the
capacity of a single memory chip (a 1-megabit chip; you need eight chips plus an optional
ninth parity-checking chip to get 1 megabyte of memory), the throughput of a network (4 megabits per
second), and the transfer speed of a hard disk (5 megabits per second).
megahertz (MHz) One million cycles per second, typically used in reference to a computer's clock
rate. Both
the clock rate and the processor type (80286, 80386, etc.) determine the power and speed of a computer.
memory A device that stores data in a computer. Internal memories are very fast and are either
read/write
random-access memory (RAM) or read-only memory (ROM). Bulk storage devices are either fixed disk, floppy
disk, tape, or optical memories; these hold large amounts of data, but are slower to access than internal
memories. See also expanded memory, extended memory, RAM, ROM
MHz See also megahertz
Micro Channel architecture (MCA) The basis for the IBM Micro Channel bus, used in high-end models
of
IBM's PS/2 series of personal computers. See also EISA
microprocessor An integrated circuit (IC) that communicates, controls, and executes machine
language
instructions.
microsecond 1/1,000,000 (one-millionth) of a second.
millisecond (ms) 1/1,000 (one-thousandth) of a second. Hard disks are rated in milliseconds.
Modern laptop
hard disks have drives of 20 to 40 milliseconds, meaning they can find the average piece of data in
1/25 to
1/50 of a second. Older hard disks were about 100 milliseconds. Higher numbers mean slower performance.
modem A combination of the words modulate and demodulate. A device that allows a computer to
communicate with another computer over telephone lines.
multimedia The presentation of information on a computer using sound, graphics, animation, video,
and text.
N
nanosecond 1/1,000,000,000 (one-billionth) of a second. Memory chips are rated in
nanoseconds, typically 80 to 150 nanoseconds. Higher numbers indicate slower chips.
NetWare A popular series of network operating systems and related products made by Novell.
network A continuing connection between two or more computers that facilitates sharing files
and resources.
O
online/offline When connected to another computer via modem and telephone lines, a modem is said
to be
online. When disconnected, it is offline.
operating system (OS) A set of programs residing in ROM and/or on disk that controls communications
between components of the computer and the programs run by the computer. MS-DOS is an operating
system.
OS/2 (Operating System/2) An operating system developed by IBM and Microsoft for use with Intel's
microprocessors. Unlike its predecessor, DOS, OS/2 is a multitasking operating system. This means many
programs can run at the same time.
OS/2 Extended Edition IBM's proprietary version of OS/2; it includes built-in communications
and database-management facilities.
P
parallel port A port that transmits or receives 8 bits (1 byte) of data at a time between the
computer and
external devices. Mainly used by printers. LPT1 is a parallel port, for example.
PCL (printer command language) Usually refers to Hewlett-Packard laser printers. Most H-P compatibles
support PCL 4. H-PÆs newest printers (the III series) use PCL 5, which includes scalable fonts
and
monochrome support for HPGL.
peripheral A device that performs a function and is external to the system board. Peripherals
include
displays, disk drives, and printers.
pixel A pixel is the smallest information building block of an on-screen image. On a color monitor
screen,
each pixel is made of one or more triads (red, green, and blue). Resolution is usually expressed in
terms of the
number of pixels that fit within the width and height of a complete on-screen image. In VGA, the resolution
is
640 by 480 pixels; in SuperVGA, it is 800 by 600 pixels.
platter The actual disk inside a hard-disk drive; it carries the magnetic recording material.
All but the thinnest
disk drives have multiple platters, most of which have two sides that can be used for data storage.
(On
multiple-platter drives, one side of each platter is usually reserved for storing control information.)
port The channel or interface between the microprocessor and peripheral devices.
program See application software
programming language Any artificial language that can be used to define a sequence of instructions
that
can ultimately be processed and executed by the computer.
PROM (programmable read-only memory) A (usually) permanent memory chip programmed after
manufacture (unlike a ROM chip). EPROMs (erasable PROMs) and EEPROMs (electrically erasable PROMs)
can be erased and reprogrammed several times.
protocol Rules governing communications, including flow control (start-stop), error detection
or correction,
and parameters (data bits, stop bits, parity). If they use the same protocols, products from different
vendors
can communicate.
R
RAM (random-access memory) Also known as read-write memory; the memory used to execute application
programs. See also memory
RAM disk VDISK (virtual disk) that can be used in place of a hard or floppy disk for frequently
accessed
files. A RAM disk is dangerous for storing data because the contents are lost if the computer crashes
or if
power is turned off. Most users
with extra RAM use it for a disk cache rather than as a RAM disk. See also memory
read/write head The part of the hard disk that writes data to or reads data from a platter.
It functions like a
coiled wire that reacts to a changing magnetic field by producing a minute current that can be detected
and
amplified by the electronics of the disk drive.
refresh rate See vertical frequency
RGB (red, green, blue) The triad, the three colors that make up one pixel of a color monitor.
See also triad
RLL (run length limited) A hard-disk method of encoding information magnetically that uses a
scheme
(GCR) to store blocks of data instead of single bits of data. It allows greater storage densities and
higher
transfer speeds than the other method in use (MFM).
ROM (read-only memory) The memory chip(s) that permanently store computer information and
instructions. Your computer's BIOS (basic input/output system) information is stored in a ROM chip.
Some
laptops even have the operating system (DOS) in ROM.
RS-232C An electrical standard for the interconnection of equipment established by the Electrical
Industries
Association; the same as the CCITT code V.24. RS-232C is used for serial ports.
S
SCSI (small computer system interface) A system-level interface designed for general purpose
applications
that allows up to seven devices to be connected to a single host adapter. It uses an 8-bit parallel
connection
that produces a maximum transfer rate of 5Mb per second. The term is pronounced "scuzzy."
sector The basic storage unit on a hard disk. On most modern hard disks, sectors are 512 bytes
each, four
sectors make up a cluster, and there are 17 to 34 sectors in a trackùalthough newer drives may
have a
different number of sectors.
serial port The "male" connector (usually DB-9 or DB-25) on the back of your computer.
It sends out data
one bit at a time. It is used by modems and, in years past, for daisy-wheel and other printers. The
other port
on your computer is the parallel port, which is a "female" connector. It is used for printers,
backup systems,
and mini-networking (LANs). See also COM.
shadow mask Inside the color monitor just behind the screen, it is drilled with small holes,
each of which
corresponds to a triad. The shadow mask helps guide the electron beams so that each beam hits only one
phosphor dot in the triad.
shell A piece of software providing direct communication between the user and the operating
system. The
main inner part of the system, called the kernel, is enclosed by the shell program, as in a nut.
slot mask Also known as an aperture grille, it serves the same function as the shadow mask on
a monitor.
spindle One part of a hard disk, around which the platters rotate.
software Programming tools such as languages, assemblers, and compilers; control programs such
as
operating systems; or application programs such as electronic spreadsheets and word processors. Software
instructs the computer to perform tasks. See also application software
spreadsheet An application commonly used for budgets, forecasting and other finance-related
tasks. Data
and formulas to calculate those data are entered into ledger-like forms (spreadsheets or worksheets)
for
analysis, tracking, planning, and evaluation of impacts on economic strategy.
synchronous communication Fixed-rate serial communication, eliminating the need for transmitting
inefficient start-stop information. PC-to-mainframe communication may be synchronous; most PC-to-PC
communication is asynchronous. Most laptop modems are asynchronous only. If you're not sure whether
you need a synchronous-asynchronous modem, you probably don't.
system-level interface A connection between the hard disk and its host system that puts control
and
data-separation functions on the drive itself (and not on the external controller). SCSI and IDE are
system-level interfaces.
T
telecommunication Using your computer to communicate with another computer via telephone lines
and
your modem.
track The circular path traced across the spinning surface of a disk platter by the read/write
head inside the
hard-disk drive. The track consists of one or more clusters.
track buffer Memory sometimes built into disk-drive electronics, sufficient to store the contents
of one full
track. This allows the drive to read the entire track quickly, in one rotation, then slowly send the
information
to your CPU. It eliminates the need for interleaving and can speed up drive operation.
transfer rate The speed at which a disk drive can transfer information between its platters
and your CPU.
The transfer rate is typically measured in megabytes per second, megabits per second, or megahertz.
transmission speed See baud rate
triad Three phosphor-filled dots (one red, one green, one blue) arranged in a triangular fashion
within a
monitor. Each of the three electron guns is dedicated to one of these colors. As the guns scan the screen,
each active triad produces a single color, which is determined by the combination of excited color dots
and
by how active each dot is. See also RGB
U
utility program A program designed to perform maintenance work on a system or on system components,
e.g. a storage backup program, a disk and file recovery program, or a resource editor.
V
V. The CCITT international communications standards, pronounced "vee-dot." Various
V. standards cover
speed (modulation), error correction, data compression, and signaling characteristics.
vertical frequency This is also called the vertical refresh rate, or the vertical scan frequency.
It is a monitor term that describes how long it takes to draw an entire screenful of lines, from top
to bottom.
Monitors are designed for specific vertical and horizontal frequencies. Vertical frequency is a key
factor in
image flicker. Given a low enough vertical frequency (53 Hz, for example) nearly everyone will see a
flicker
because the screen isn't rewritten quickly enough. A high vertical frequency (70 Hz on a 14-inch monitor)
will
eliminate the flicker for most people.
VGA IBM's third (1987) and current mainstream graphics standard, capable of 640-by-480-pixel
resolution at
16 colors or gray shades. SuperVGA (800 by 600) resolution is important on desktop PCs. A handful of
laptops support SuperVGA when connected to an external monitor; they use regular VGA when driving the
built-in display. Some laptop vendors use "text mode" VGA, which means the monitor displays
only 400
pixels, not 480, vertically, and uses double-scan CGA (640 by 400) for graphics.
VRAM (video random-access memory) Special-purpose RAM with two data paths for access, rather
than the
one path in conventional RAM. The two paths let a VRAM board handle two functions at once: display
refresh and processor access. VRAM doesn't force the system to wait for one function to finish before
starting the other, so it permits faster operation for the video subsystem.
W
wide area network (WAN) Usually a moderate to large network in which communications are conducted
over
the telephone lines using modems.
write protection Keeping a file or disk from being written over or deleted. 3 1/2-inch floppy
disks use a sliding
write-protect tab in the lower-left corner (diagonally across from the beveled corner of the disk) to
keep the
computer from writing to the disk. When the opening is hidden by the tab (no light passes), you can
write to
the disk; tab open, you can't write. This can be confusing because it's the exact opposite of how a
5 1/4-inch
disk works. Most file management utilities allow you to write-protect individual files.
X
XMA (extended memory specification) Interface that lets DOS programs cooperatively use extended
memory
in 80286 and higher computers. One such driver is Microsoft's HIMEM.SYS, which manages extended
memory and HMA (high memory area), a 64K block just above 1MB.
| 
