Quincy Center for Technical Education
Computer Technology Department
Computer Definitions
A B C D
E F G H
I J K L
M N O P
Q R S T
U V W X Y Z
A
- address: A location in memory.
- address bus: The electrical pathway over which addressing information
is sent.
- Arithmetic-logic unit:The central processor of the CPU; that part of
the CPU that carries out numerical calculations and logical
comparison.
B
- backplane: See motherboard.
- base-2: The number system built on a root of 2; the numerical basis
of a digital computer operations. See binary.
- baud rate: The transfer of data bits in bps.
- binary: (1) The base-2 number system. (2) A two-choice system
represented by the digits 1 and 0, which can stand for "yes"
and "no," "on" and "off," "go" or "no go," etc.
- bit: Binary digit, 1 or 0; the fundamental unit of digital data.
- boot: Short for bootstrap, the (1) process whereby the computer is
brought to operating status, and (2) the program for
accomplishing this end.
- bus: An electrical pathway. In a typical computer, there are four:
address bus, data bus, control bus, and power bus.
- byte: Eight bits in a coherent string.
C
- central processing unit (CPU): The system of circuits that controls the
basic operations of a computer, commonly a single IC called
microprocessor; see also MPU.
- character: Any symbol : alphabetic, numeric, etc.
- checksum: Summation check, a method of checking for the accuracy of
transmitted data.
- chip: An integrated circuit.
- clock: (1) the timing system that keeps the computer operations
organized; (2) an add-on device that keeps "real time," just
like a wristwatch, hence the real-time clock.
- code: The representation of meanings with symbols. In computer
usage, the term usually means program material.
- compatibility: The ability of one computer to run the programs written
for another computer.
- control bus: The electrical pathway over which the clock and other
control signals are sent.
- Cyclic redundancy check (CRC): An error-checking method, often used in disk
operating systems.
D
- data: Information entered into and retrieved from a computer.
- databit: See bit.
- data bus: The electrical pathway over which databits are sent,
generally a byte or a word at a time.
- data transmission: The movement of data from one part of the computer
to another, or from one computer system to another. To
achieve successful communication, both sides of the
communication loop must follow the same communication
protocols for data transmission rate an handshaking, and
certain other parameters.
- diode: A semiconductor device that allows electricity to flow in one
direction but not the another, a process called
rectification. See rectifier and zener.
- disk: Any of several types and sizes of disk-shaped magnetic
storage media.
- disk drive: An electromechanical device for reading from and writing
to disks.
- disk operating system: A program, stored mainly on disk, for
controlling the normal operations of a computer. CP/M, MS-
DOS, and UNIX are examples of currently popular disk
operating systems.
- dot pitch: The width of pixel spacing. Smaller is better. A figure in
the neighborhood of .3mm is acceptable.
- dual-in-line package: A method of packaging electronic components,
particularly ICs, such that there are two parallel rows of
pins for insertion into holes or into sockets mounted on a
printed circuit boards.
- dump: Displaying some (or all) of the contents of memory on a
display device (usually a video monitor or a printer) with
debugging or other programmer's utilities. The dump is most
commonly done in hexadecimal numbers.
E
- edgecard connector: A connector arrangement whereby the circuit board
provides a male mating element as a part of the board itself
and etched with several fingers that match with connectors in
the female element, slot on another board or a cable. Also
called card-edge connector.
- expansion slot: A connector--usually on the main circuit board of a
computer--designed to accept memory boards and other circuit
boards that enhance the basic capabilities of the computer.
F
- firmware: Program material permanently fixed in the ROM type of memory
chips. See monitor.
- floppy disk: A flexible magnetic disk permanently sealed in a thin
plastic envelope. The first floppies were eight inches in
diameter. Now 5 1/4-inch and 3 1/2-inch sizes predominate.
- formatting: The process of preparing a disk or other magnetic medium
for use by writing certain information to the disk. The
formatting routine establishes the electrical identity of
tracks and sectors.
G
- garbage: Useless, unwanted, meaningless information; generally the
result of a computer or software malfunction.
- gate: An electrical circuit (mainly transistors) used to control
the flow of databits in a computer to produce desired
arrangements of these bits. Integrated circuits consist
mainly of gates.
H
- handshaking: The establishment and maintenance of data transfer between
two devices by a set of signals specifying that one device is
ready to send and the other is ready to receive data .
Handshaking can be accomplished in two ways: via control
codes sent on the transmit and receive lines (software
handshaking) or via separate lines (hardware handshaking).
- hardcopy: ASCII-coded and graphics data printed on paper or a plotter.
- hard disk: A nonflexible disk-shaped magnetic storage medium, also
called fixed disk and Winchester.
- hardware: Equipment: computer, printer, video unit, etc.
- head: The electromagnetic read/write (playback/record) element of a
disk drive. A magnetic flux is produced across the head gap,
a narrow region between the electromagnetic poles.
- head stepper: The stepper motor that moves the head back and forth
across the surface of a disk during read/write operations.
- heat sink: A heat-dissipating metal device (usually finned) mounted on
electronic components that tend to get very hot (e.g.,
voltage regulators.)
- hexadecimal: Number base-16, consisting of alphanumeric digits
0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,f. Commonly used in assembly
language programming because of its convenience. Very large
numbers can be represented by a small number of hex digits,
for example, 1111111111111111 (base-2) = 65,535 (base-10 =
FFFF (base-16). Further, like octal, hex is both byte- and
powers-of-2-oriented.
I
- integrated circuit: Highly miniaturized electronic circuitry fabricated
in a specially prepared silicon. Degrees of miniaturization,
hence component density, are given terms like large-scale
integration (LSI) and very large-scale integration (VLSI).
The silicon chips are sealed in plastic or ceramic packages
and typically provided with two parallel rows of pins for
insertion into printed circuit boards. This type of chip unit
is called a DIP, Dual Inline Package.
- interface: The circuitry needed to establish communications between two
different pieces of electronic equipment, such as a computer
and a printer.
- input/output: The process of getting data into and out of a computer. A
keyboard is a representative input device; a video display is
a representative output device.
J
- jack: A socket, such as that on a video monitor, for receiving the
video cable plug.
- junction: The region in a semiconductor where the p-type material meets
the n-type material. This is the region where transistor
action occurs.
K
- kilo-: (1) As a prefix in designations of computer memory size,
1,024 (thus, one kilobyte = 1,024 bytes). (2) As a prefix in
other numerical designations; 1,000, thus, one kilovolt =
1,000 volts.
L
- least significant bit: The "rightmost" bit of a byte or computer word,
the bit with the least numerical weight.
- least significant byte: The "rightmost" byte of a computer word, the
byte with the least numerical weight. Sometimes called the
low-order byte.
- least significant digit: The "rightmost" digit, the digit with the
least numerical weight.
M
- mass storage: General term for disk, tape, and other external storage
systems.
- mega-: (1) As a prefix in designations of computer memory size,
1,048,576; thus, one megabyte = 1,048,576 bytes. (2) As a
prefix in other numerical designations, 1,000,000; thus, one
megawatt = 1,000,000 watts.
- memory: The region in a computer into which data is stored and
retrieved in order for the computer to carry out its
activities. Each location in memory has a unique address.
Some addresses are reserved for the computer's own use, but a
large block is available for user programming or applications
software. See memory map. The memory of a computer is
located in banks of RAM (random-access memory) and in ROM
(read-only memory). Most of the RAM is open; the ROM is
reserved.
- memory map: (1) The way in which memory is allocated in a particular
computer system; (2) a printed representation of this
allocation.
- main processing unit: Another name for the CPU or microprocessor.
- microprocessor: Commonly called the CPU, a highly complex integrated
circuit used to control the basic operations of a computer.
Some microprocessors act as slaves or coprocessors, taking
over certain processing function to speed up overall
operational efficiency, hence speed.
- monitor: (1) A program permanently set into one or more ROMs designed
to control certain operations of the CPU; can be said to act
as an intermediary between the computer user and the CPU; (2)
a video display unit.
- most significant bit: The leftmost bit of a byte or computer word, the
bit with the greatest numerical weight.
- most significant byte: The leftmost byte of a computer word, the byte
with the greatest numerical weight; sometimes called the
high-order byte.
- most significant digit: The leftmost digit, the digit with the greatest
numerical weight.
- motherboard: The main system board in a computer, containing the basic
circuitry as well as slots for expansion boards. Sometimes
erroneously called the backplane, which is really just the
set of system bus connections in certain types of computers.
- multiplexing: The process whereby, a single resource is time shared for
several applications more or less simultaneously. Many
networks use some form of multiplexing. At the chip level,
two different signals can be multiplexed on a single bus,
effectively allowing the chip to perform two different
function or manage two packets of data at the same time. The
two signals or packets are split apart by a demultiplexing
process.
N
- network: A system of linking computers and/or terminals in a way that
allows them to share common resources (e.g., large capacity
hard disk) and to work at several different tasks
concurrently.
- n-type material: Semiconductor material rich in electrons; negatively
charged material.
O
- octal: Base-8 number system. Numerals are 0,1,2,3,4,5,6,7. See
hexadecimal.
P
- peripheral: Any external equipment used to expand the capabilities of
the computer and its convenience to the operator. Printer,
plotter, spooler, etc.
- pixel: Picture element, a single point on a video screen. The number
of pixels a video monitor can display is one measure of its
resolution. The greater the number of small clumps of pixels
(ideally, single pixels) the computer can control, the
sharper the picture.
- port: A gateway in a computer through which data is transmitted.
The printer port connector, for example, is the user-
accessible hardware manifestation of the computer's parallel
or serial port. Each port has its own address in the memory
management scheme of the computer.
- power: Electricity for running the computer. Compare signal.
- power bus: The electrical pathway over which the electrical power for
running the computer travels, starting at the computer power
supply.
- printed circuit board: A board in which the wiring for the one or more
electronic circuits provided for results from etching a
copper coating. Etching leaves behind copper traces
representing the basic circuit interconnections. The board is
drilled and marked for the insertion of the electronic parts-
-ICs, resistors, capacitors, etc. --that constitute the
circuit.
- program: A set of instructions written in a language for the purpose
(i.e., a programming language) and designed to cause a
computer to perform useful function at the will of the user.
The form of the instructions is called code. Someone who
turns a program design into specific lines of code is called
a coder. The programmer and the coder may be the same
person.
- programming array logic: This type of IC can be feild-programmed for
"instant upgrades" or certain on-the-spot engineering changes
in a system design. Bears a certain resemblance to the ROM in
the programming hardware required, but is different in that
PALs are not merely memory devices, but customizable gate
arrays.
- p-type material: In a semiconductor, the positively charged or hole-
rich material.
Q
- queue: The waiting line; term can apply to instructions awaiting
processing by the CPU or to the files of text waiting to be
printed.
- qwerty: The standard typewriter/computer keyboard arrangement for the
letters of the alphabet and the numerals.
R
- random access: Getting at data stored in memory or in a mass storage
device by no fixed rules of precedence. One type: bypassing
the CPU to go directly to memory (direct-memory access).
- raster: The pattern of scanning lines on a video display tube.
- read-only memory: (1) a type of memory IC that can be read from, but,
once it has been (factory) programed , not written to; (2)
the computer firmware that uses this type of memory.
- rectifier: A device commonly made of diodes for turning AC into DC.
Because of the ability of a diode to allow current to flow on
only one direction, the rectifier prevents half of the AC
sine wave from flowing in the circuit. A flow of electricity
consisting of only one half of the sine waves is called
rippling DC, which must be filtered to be useable by most
electronic equipment. A bridge rectifier consists of four
diodes connected (full-wave rectification) and still produce
DC.
- register: Registers are temporary storage and data manipulation areas
in a microprocessor, called by such names as accumulator,
index register, segment register, instruction register, and
others.
S
- scan rate: The speed at which the electron beam scans from the top to
the bottom of the video display. American TV scans at the
"official" rate of 525 lines per second. More lines provide
better resolution.
- screen dump: A literal printout (hardcopy) of the material currently
visible on the video screen.
- semiconductor: A device, usually made of a silicon-based material, that
can be made to conduct or to block electricity. See
transistor, diode, n-type material, and p-type material.
- sensor: An external analog device that reads "real world" values like
temperature and moisture and transduces them into voltages
for processing by an analog-to-digital converter. A
transducer changes one form of energy into another form.
- signal: Electricity of very low power used for the data processing
and control operations of a computer. All the internal
signals take the form of binary digits, 1 and 0, manifested
as voltages (at negligible current), 0 to .8VDC for binary 0,
2 to 5VDC for binary 1.
- sine wave: The characteristic curve of alternating electrical current
(AC). One cycle, which consists of a positive and a negative
swing, adds up to 360 degrees, that is , a complete circle.
But since the wave is moving in time, a sine-wave plot
appears as a series of peaks and valleys.
- software: Program material, including programs to write programs.
Software can be input via data-entry devices (keyboard,
optical scanner, etc.), mass storage (disk, tape, CD-ROM,
etc.), and plug-in cartridges, which are circuit boards
containing firmware.
- speech recognition system: A computerized speech system capable of
acting predictably on spoken commands.
- speech synthesis system: A system capable of producing understandable
imitations of human speech.
- stepper motor: A motor capable of moving in small, precise increments,
used, for example, in disk drives to move the head and, in
printers to move the paper-advance mechanism (platen or
tractor).
- syntax: As applies to programming, the accepted usages of the
programming language. For example, misspelling a command or
statement in a programming language will result in a "syntax
error" message.
T
- terminal: A computer slaved to another computer, or a video display
device with no computing capabilities of its own, though
perhaps provided with one or more interfaces for data
communication.
- trace: An electrical interconnect ("wire") on a printed circuit
board.
- transducer: A device that converts one form of energy into another. A
temperature transducer changes the registered temperature
value into a voltage value; a loudspeaker changes voltages
into sounds.
- transistor: A semiconductor device; the fundamental electronic element
of most ICs, where transistors act as switches to form gates.
Transistors are also discrete devices used for switching, and
current or voltage amplification. Any simple transistor
consists of three electrodes: collector, emitter, and base.
The base acts as the toggle for switching the transistor on,
or as the controller for the transistor's output at any given
moment.
U
- utilities: Programs designed to facilitate the use of the computer
system.
V
- video bandwidth: Bandwidth identifies a range if frequencies used for
some particular purpose. In the case of video, the higher the
frequency bandwidth, the more detail can be transmitted. A
good-quality color monitor should have a bandwidth no lower
than 15 MHz.
- volatile memory: Memory that will not hold data after the power has
been shut off; the normal state of affairs in the memory of
most computer systems. In some desktop computers, memory is
retained by a battery backup system after the main power is
turned off. Contrast volatile memory with mass storage.
- voltage regulator: An integrated circuit designed to maintain voltage
at a fixed level. Most microcomputers use voltage regulators
that are rated at + 5V and +12V.
W
- word: In microcomputers, two bytes as a coherent unit constitute a
word-not to be confused with words in ordinary language. A
word is divided into a low-order byte and a high-order byte,
the former containing the least significant bit, the latter
the most significant bit.
X
- X-Y plotter: An ordinary plotter, capable of locating points along the
vertical (X) axis and horizontal (Y) axis.
Y
- yoke: The electromagnetic coil around the neck of a CRT, used for
truing the picture horizontally and adjusting color purity.
Not to be fooled with by amateurs!
Z
- zener diode: A type of diode, also known as a breakdown diode because
of its ability to avalanche when a critical voltage is
reached. This characteristic makes it useful as a protective
device. When the voltage is below the avalanche threshold,
the zener blocks the passage of electricity, but when the
voltage exceeds the critical point, the diode conducts and
the overvoltage can be directed safely to ground.