Computer
Glossary
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).
Accelerator: Term for special Windows accelerator
chips installed in graphics cards, especially in true-color cards, which
optimize the screen display in Windows.
Access time: This is the period of time necessary to
access data on the drives or in the working storage. For the hard disk, this is
how long takes the hard disk head to move to the place where the data can be
read.
A/D converter: This device is responsible for
converting analog sound waves into digital sound so that the sound card can
process it. It also reconverts digital sound from the sound card back into
analog sound waves. The A/D converter is at work when you digitize pieces of
music coming from a tape recorder with your sound card and when you play sound
files recorded digitally over the speakers.
AT bus: A 16-bit bus, which in comparison to the old
8-bit bus of XTs offers a, significantly higher data transfer rate. The AT bus,
with a bus-clock rate of 8.3 MHz reaches a data throughput rate of 2 to 6 MB
per second. When these first came out, they worked at the speed 286s, which
were the current models. With quicker PCs, the slow AT bus soon became the eye
of the needle for data inside the computer.
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: The acronym for Basic Input Output System
describes the routines stored in the ROM of the computer's motherboard. These
routines contain the most important functions of the computer, such as the
loading of the actual operating system, and the control of the hard disk, the
graphics card, or the computer interfaces. 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.
cache The cache is an intelligent read/write
memory that prepares data so that it can be accessed much faster when needed.
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++.
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.
Caddy: A caddy is a sort of jacket you must place a
CD in before you put it into the drives of some CD-ROMs. Caddies are supposed
to prevent the drive from being exposed to impurities. Many newer CD-ROMs don't
require caddies.
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
DIMM: DIMM stands for Dual Inline Memory Module. DIMM
banks are available with different memory capacities:
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.
Data transfer rate: This rate describes the
efficiency of hard disks, streamers, CD-ROM-drives, and others. It describes
the amount of data read by or recorded on a drive within a certain unit of
time, usually one second. The CD-ROM is an exception; the data transfer rate
only describes the data read by the CD-ROM.
DIP switches: These are the tiny switches that
usually appear in a row. Each switch can be in one of two positions, either on
or off. By setting up the DIP row of switches, you can define the hardware address
of many plug-in cards.
Disk drives: There are two different kinds of disk
drives: the 5.25" and the 3.5"drives. The number simply stands for
the size of the disks fitting into the drive. The two drives differ in their
memory capacity. The 5.25" drive holds 1.2 MB of data, while the smaller
3.5" drive holds 1.44 MB. There are now 3.5" disk drives that also
hold 2.88 MB.
DMA channel: Determines which channel a hardware
component (such as the sound card), uses to access the working storage read or
file data.
dpi: Short for dots
per inch. It is the measure that defines the resolution of printers and
scanners.
DSP chip: Short for Digital Signal Processor. This
chip takes over certain sound card tasks and produces certain emulations. It
can make a sound card SoundBlaster-compatible, and is can convert a digitized
sound into a general
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
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
EISA: The abbreviation of Extended Industrial
Standards Architecture, which characterizes a 32-bit wide bus system. This bus
system is the successor of the AT bus and is used by 386 and better computers.
In comparison with the conventional AT bus, it has a higher data transfer rate
(more than 20MB per second). 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
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
Feature connector: The feature connector connections
your PC to other hardware components. It is especially used for connecting a
graphics card to a video overlay card (to digitize video sequences). In this
case, the video signal of the overlay card is linked up with the VGA signal.
Font Cartridge: These are extension cards that are
inserted directly into laser jet printers to increase the number of the
printer's type fonts. Compared with Windows fonts, these printer fonts can be
printed much faster.
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.
Gameport: A special
interface to which joysticks or input devices for computer games can be
connected.
GDI printer: GDI is short for Graphical Device
Interface. It usually characterizes the screen displayed to you by Microsoft
Windows. A GDI printer prints exactly what you see on your screen. This kind of
printer does not need its own printer memory, since it uses the system memory.
In addition, a GDI printer is very easy to operate.
Graphics card BIOS: Like the system BIOS, this
contains important program routines, but it also organizes video memory.
Moreover, the graphics card BIOS is also responsible for generating the
displayed character sets.
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.
Host Adapter BIOS: The controller BIOS turns the SCSI
host adapter into an intelligent device and (like the system BIOS) contains important
fixed program routines. The BIOS makes sure that the SCSI host adapter requests
information about additional new drives and identifies the installed drives.
IO address: This is the hardware address by which the
CPU addresses hardware components.
IRQ: Also called interrupt, this is a small
routine that allows a hardware component function (such as.
a sound card) to interrupt the working process of the CPU.
ISA: ISA bus is the standardized form of the AT bus.
IDE (integrated drive electronics) A disk drive with
its own controller electronics built in to save space and money. Many laptops
use IDE drives.
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.
Jumper: These are small plug-in bridges encased in
black plastic. They enable certain functions to be operated on hardware
components such as hard disks. For an AT bus hard disk, jumpers configure one
hard disk as master and the other as slave.
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).
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.
LPT port: LPT stands for the parallel
interface, an interface with which data can be transferred by bytes either into
or out of the computer. The printer is usually attached to this port. Up to
three LPT interfaces can be operated in MS-DOS.
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.
Modulator/demodulator (modem): This is a component
you attach to your telephone to send data over a phone line. It converts output
information into electrical pulses and modulates them on the carrier frequency,
in this case the telephone line. It also records input electrical pulses and
converts it into analog information.
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.
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.
Optical mouse: With the optical mouse, the movements
of the mouse and the pressure on the keys are being transmitted via infrared
light to the PC, eliminating bothersome cables.
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-PĘs 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.
PCI: This is the newest bus system, which is most
often used with the Pentium processor and newer 486s. The bus system has a
width of 32 bits and the CPU's clock rate.[**AU:
unclear**] It is supposed to reach a data transfer rate of 100 MB per second.
PostScript: A vector-oriented printer font from
Adobe. The PostScript format is a high-quality format that can be output by any
PostScript printer. While the laser jet printer reaches 300-600 dpi, it is
output with 1500 to 3500 dpi by exposers.
Printer memory: Laser jet printers have a memory in
where the pages to be printed are built up. Smaller laser jet printers come
with 512 KB of memory, which can soon lead to a memory shortage if you are
processing graphics. A page-sized graphic requires 1 MB of printer memory at
300 dpi.
Processor: Another term for CPU. CPUs are classes
according to their efficiency: 286, 386-SX, 386-DX, 486-SX, 486-DX, 486-DX2,
486-DX4, and Pentium. The 286 possesses an internal and external 16-bit data
bus and a 24-bit address bus. The latter allows the 286 a direct addressing of
up to 16 MB of working storage. The clock frequencies of the 286 begin at 6 or
8 MHz and go up to10 or 12 MHz. The 386-DX was the first 32-bit processor with
clock rates of 16, 20, 25, and later 33 MHz. The 386-SX is the cheap version of
the 386-DX. Internally, it works with the 32-bit data bus, but externally it
uses the 16-bit bus of the 286. Then came the 486-DX,
with clock rates of 25, 33, and 50 MHz. It also uses a 32-bit data bus and has
the advantage of a coprocessor, a cache controller, and two large cache
memories with 4 KB each already integrated. The cheap version, the 486-SX,
lacks the integrated coprocessor. The internal clock rate of the DX2
(486-DX2-50 and 486-DX2-66) and the DX4-processors was doubled and tripled,
respectively. These processors externally work with clock rates of 25 and 33
MHz respectively. The latest development is the Pentium processor, which also
works with an address bus of 32 bits. Its data bus contains 64 bits, though, so
that the Pentium can also access the working storage with 64 bits.
PS/2 SIMM: These were originally built for the IBM
PS/2-computers and do not fit into the conventional SIMMs. Today they are also
used for the VLB and PCI boards of other manufacturers, since they allow 32-bit
access to the working storage. The access rate is also dependent on the
operating system, though. While OS/2 supports 32-bit-access, Windows 3.1 does
not.
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.
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
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.
RAM: RAM stands for Random Access Memory, the
working storage of your PC. The contents of the working storage can be read or
changed at will. The content is volatile, though, which means that it gets
destroyed if the system crashes or is switched off. You always have to write
(or store) the content of the working storage to the hard disk before switching
the computer off.
Refresh rate: Determines the number of complete
screen refreshings per second. With a minimal refresh
rate (non-interlaced) of 72 Hz, the display image appears totally stable to our
eyes. Non-interlace mode means that the graphics card always builds up a
full-screen display. With the interlaced mode, on the contrary, only
half-screen displays are being built up on the monitor at a high frequency,
which reduces the image quality.
S3 graphics chip: The S3 chip is one of the most common
32-bit graphics chips. It is a Windows accelerator chip, and its job is the
optimization of the screen display in Windows. The newest version of the S3
chip addresses a video memory of 4 MB. Its maximum resolution lies at 1600 x
1200 pixels with 256 colors. This chip manages a true-color display up to a
screen resolution of 1024 x 768 pixels. Moreover, this chip is able to play
back AVI videos.
SIMM: Like the PS/2 SIMM, the SIMM extends the
working storage. SIMM banks are available with different memory capacities: 1
MB, 4 MB, 8 MB, and recently with 16 MB. There are usually eight slots on the
motherboard vacant for these SIMM banks. With some boards, the slots always
need to be filled with banks of the same memory capacity. Other boards do not
have this restriction.
Synthesizer: This is a chip on the sound card that
converts a digital sound from the sound card into the corresponding
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 trackłalthough
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.
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
Trackball: This is a device that works similarly to a
mouse. This device has specific keys for single- and double-clicks, and the
device itself doesn't move. To move the pointer on-screen, you move the ball
that is attached to the device. The trackball is advantageous if you do not
have a lot of space, since you don't need any room for moving the mouse.
True-color: This is the realistic display of color
on-screen. True-color display can only be achieved with a color intensity of 24
bits, which is 16.7 million colors. True-color cards
are graphic cards that can concurrently display this many colors.
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.
Vesa Local Bus: High-speed
expansion bus. Runs at 33 MHz speed and transfers 32 bits per operation.
Video memory: The video memory a graphics card
requires is determined by the resolution and the color-intensity this specific
card manages to perform. The memory capacity necessary to get a certain screen
resolution can be determined easily by multiplying the resolution of a column
by that of a line. For 1024 x 768 pixels, the memory requirements would be
786,432 bits. This sum has to be multiplied again by the color intensity (e.g.,
8 bits in the case of 256 colors 786,432 x 8 = 6,291,456
bits). Since the video memory capacity is always expressed in KB, you now have
to divide the previously calculated number first by 8 (8 bits are equivalent to
1 byte) and then again by 1024 (1024 bits are equivalent to 1 KB). In this
example, you get 768 KB, which means that a graphics card with a video memory
capacity of 1 MB can display the mentioned resolution with 256 colors. If a
graphic card uses DRAM components (dynamic storage modules), the screen build
takes longer, since these components are slow and do not allow high refresh
rates. Professional graphics cards use the more expensive but faster VRAM
components.
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.
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.
Wavetable ROM: This chip (which gives the name to the
new Wavetable cards) contains the equivalent sounds of more than 100 musical
instruments. This chip makes it possible for Wavetable cards constructed like
16-bit sound cards to produce a realistic concert hall experience. You must
have additional software to support the Wavetable format.
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.