- cited from Microsoft Press — Computer Dictionary Second Edition The Comprehensive Standard for
Business, School, Library, and Home (1994)
- acronym
- A "word" derived from the first or most important letters in a multiword descriptive noun or
other expression, often serving as a mnemonic whose letters recall the actual words in the term.
Computer terminology is rife with acronyms; three of the most common are BASIC (Beginners'
All-purpose Symbolic Instruction Code), RAM (random access memory), and DOS (disk
operating system). Some acronyms become words in their own right; "laser," for example, used
to be written LASER, for Light Amplification by Stimulated Emission of Radiation.
- adder
- A unit within a central processing unit (CPU) that sums two numbers sent to it by processor
instructions; any circuit that adds binary values. Also, a circuit or integrated circuit that sums the
amplitude of two input signals.
- address
- As a noun, the value that represents an individually accessible storage location. In a typical
computer, each memory location has a separate address. The addresses for the memory system are
numbered 0, 1, 2, and so on, up to the maximum possible number of locations supported. Some
addresses, having no associated storage in the form of RAM, correspond to input or output ports
so that data can be read from or written to only those locations.
As a verb, to reference a storage location.
- address bus
- A hardware pathway, typically consisting of from 20 to 64 separate lines, that carries the
signals specifying locations in a computer's memory. The address bus enables the microprocessor
to select a specific location in memory for transfer of data via the data bus. The size of (number of
lines in) the address bus is directly related to the number of locations amicroprocessor can address
? essentially, the amount of memory it can use for programs and data.
- address register
- A small, high-speed portion of memory within a microprocessor, dedicated to temporarily
holding a memory address, either in whole or in part, so that information can be transferred
accurately to and from an exact location.
- address space
- The range of memory locations to which a microprocessor can refer; effectively, the amount
of memory a microprocessor could use if it were all available. The 8088 microprocessor in an
IBM PC, for example, is capable of addressing 1 megabyte (about 1 million bytes) of storage; the
68040 and i486 microprocessors can address about 4 gigabytes (4 billion) bytes. A computer's
address space holds not only application programs and data but also the operating system and
various types of "housekeeping" information such as reserved areas for transferring data to and
from the I/O ports and the disk drives. The size of the address space is determined by the
capabilities of the microprocessor and by the size of the address bus (pathway) that carries the
signals representing unique addresses, or locations, in memory.
- algorithm
- In the most general sense, any set of instructions that can be followed to carry out a
particular task. For example, a recipte in a cookbook could be considered an algorithm. In
computer usage, an algorithm can usually be explicitly encoded in a set of computer language
instructions that manipulate data of some sort. There are many volumes of published algorithm
covering a wide range of topics and applications, which are used in programming much as a recipe
is used in cooking — as either a specific solution or a starting point for experimentation.
- analog
- A term applied to any device, usually electronic, that represents values by a continuously
variable physical property, such as voltage in an electronic circuit. Derived from the Greek word
"analogos," meaning proportion or ratio, "analog" means both variation and proportion. An
analog device can represent an infinite number of values within the range the device can handle. In
contrast, digital representation maps values onto discrete numbers, limiting the possible range of
values to the resolution of the digital device.
- AND
- A logical operation for combining two bits (0, 1) or two Boolean values (false, true). It
returns the value 1 (true) if, and only if, both values are 1 (true). The possible combinations are
shown in the following table:
| a | b | a AND b |
|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
- AND gate
- A type of digital circuit that outputs a 1, or true, only when all inputs are 1. The truth table
shows the results of all possible combinations of two input signals (1=true, 0=false) for such a
gate.
- ANSI
- Pronounced "ann-see." Acronym for the American National Standards Institute, an
organization of American industry and business groups dedicated to the development of trade and
communication standards; internationally, the American representative to the International
Organization for Standardization. In the microcomputer field, ANSI is commonly encountered in
three areas: programming languages, the SCSI interface, and the ANSI.SYS device driver. ANSI
standard programming languages, such as FORTRAN, COBOL, and C, are those that conform to
ANSI recommendations designed to eliminate variations that could cause problems in transporting
a program from one type of computer system or environment to another. The SCSI interface is a
high-speed parallel interface used to connect devices to Apple Macintosh and other
computers.
- application
- A computer program designed to help people perform a certain type of work. An application
thus differs from an operating system (which runs a computer), a utility (which performs
maintenance or general-purpose chores), and a language (with which computer programs are
created).
- ALU = Arithmetic/Logic Unit
- The computer's circuitry for arithmetic, comparative, and logical functions. The ALU is an
integral part of the computer's microprocessor chip.
- AI = artificial intelligence
- The branch of computer science that deals with enabling computers to emulate such aspects
of intelligence as speech recognition, deduction, inference, creative response, the ability to learn
from past experience, and the ability to make reasonable inferences from incomplete information.
- ASCII file
- Also called a text file, a text-only file, or an ASCII text file. A document file in the
universally recognized text format called ASCII (American Standard Code for Information
Interchange). An ASCII file contains characters, spaces, punctuation, carriage returns, and
sometimes tabs and an end-of-file marker, but it contains no formatting information. This generic
format is sometimes referred to as "text" and is useful for transferring unadorned but readable files
between programs that could not otherwise understand each other's documents.
- assembly language
- A type of low-level programming language in which each statement corresponds directly to a
single machine instruction. Assembly languages are thus specific to a given processor. After
writing an assembly language program, the programmer must use the assembler specific to the
processor to translate the assembly language into machine code. Assembly language provides
precise control of the computer, but assembly language programs written for one type of computer
must be rewritten to operate on another type. Assembly language might be used instead of a high
level language for any of three major reasons: spped, control, and preference. Programs written in
assembly language usually run faster than those generated by a compiler; use of assembly language
lets a programmer interact directly with the hardware (processor, memory, display, and
input/output ports).
- bit
- Short for binary digit; either 1 or 0 in the binary number system. In processing and storage,
a bit is the smallest unit of information handled by a computer and is represented physically by an
element such as a single pulse sent through a circuit or a small spot on a magnetic disk capable of
storing either a 1 or 0. Considered singly, bits convey little information a human would consider
meaningful. In groups of eight, however, bits become the familiar bytes used to represent all types
of information, including the letters of the alphabet and the digits 0 through 9.
- Boolean expression
- An expression that yields a Boolean value (true or false); sometimes called a logical
expression or a conditional expression. Such expressions can involve comparisons (using
relational operators such as < [less than] and > [greater than]) and logical combination (using
Boolean operators such as AND, OR, XOR) of Boolean expressions.
- Boolean operator
- Also called a logical operator. An operator designed to work with Boolean values. The four
most common Boolean operators in programming use are AND (logical conjunction), OR (logical
inclusion), XOR (exclusive or), and NOT (logical negation).
- compiler
- In the most general sense, any program that transforms one set of symbols into another by
following a set of syntactical and semantical rules; in the most common sense, a program that
translates all the source code of a program written in a high-level language into object code prior to
execution of the program. Object code is executable machine code or a variation of machine
code.
- directory
- A catalog for filenames and other directories stored on a disk; a way of organizing and
grouping the files on a disk so that the user is not overwhelmed by a long list of files. All the
filenmaes belonging to a particular project, for example, might be kept together in one directory.
The topmost directory is called the root directory; the directories within a directory are called
subdirectories. Depending on how an operating system supports directories, filenames in a
directory can be viewed and ordered in various ways — for example, alphabetically, by date, by
size, or as icons in a graphical user interface. What the user views as a directory is supported in
the operating system by tables of data, stored on the disk, that contain characteristics associated
with each file, as well as the location of the file on the disk. In the Macintosh operating system,
directories are called folders.
- disc
- A round, flat piece of nonmagnetic, shiny metal encased in a plastic coating, designed to be
read from and written to by optical (laser) technology. It is now standard practice to use the
spelling disc for optical discs and the spelling disk in all other computer contexts,
such as floppy disk, hard disk, RAM disk, and so on.
- disk
- A round, flat piece of flexible plastic (floppy disk) or inflexible metal (hard disk) coated with
a magnetic material that can be electrically influenced to hold information recorded in digital
(binary) form. A disk is, in most computers, the primary means of storing data on a permanent or
semipermanent basis. Because the magnetic coating of the disk must be protected from damage
and contamination, a floppy (5.25-inch) disk or microfloppy (3.5-inch) disk is encased in a
protective plastic jacket. A hard disk, which is very finely machined, is enclosed in a rigid case
and can be exposed only in a dust-free environment.
- fetch
- The process of reading an instruction or an item of data from memory and writing it in a
register. Fetch is part of the execution cycle of a microprocessor; first an instruction or item of data
must be fetched from memory and loaded into a register, after which it can be executed (if it is an
instruction) or acted upon (if it is data).
- gate
- Also called a logic gate. An electronic switch that follows a rule of Boolean logic, such as
AND, OR, or NOT. An extremely small component of a semiconductor device, a logic gate
produces an electric output signal that is logically related to the states of one or more input signals.
For example, a logic gate designed to invert an input signal would convert the electronic equivalent
of an incoming binary 1 to a 0 or of an incoming binary 0 to a 1. Because logic gates can be
designed to perform different types of logical functions, they can be combined in various ways to
enable a computer chip to add, substract, multiply, divide, and carry our other processing
operations.
- hard disk
- One or more inflexible platters coated with material that allows the magnetic recording of
computer data. A typical hard disk rotates at 3600 RPM (revolutions per minute), and the
read/write heads ride over the surface of the disk on a cusion of air 10 to 25 millionths of an inch
deep. A hard disk is sealed to prevent contaminants from interfering with the close head-to-disk
tolerances. Hard disk provide faster access to data than floppy disks and are capable of storing
much more information. Because platters are rigid, they cvan be stacked so that one hard disk
drive can access more than one platter. Most hard disks have from two to eight platters.
- instruction set
- The set of machine instructions that a microprocessor recognizes and can execute. An
instruction set includes low-level, step-at-a-time instructions, such as add, subtract, multiply, and
divide. Each microprocessor has its own instruction set.
- IC = integrated circuit
- Also called a chip. In electronics, the packing of circuit elements, such as transistors and
resistors, onto a single chip of silicon crystal or other material. Integrated circuits are categorized
by the number of elements they hold. The larger the number of circuits packed into a given area,
the smaller they must be. At the densest levels of packing, circuit elements can be only a few
atoms in size.
- interface
- The point at which a connection is made between two elements so that they can work with
one another. In computing, different types of interfacing occur on different levels, ranging from
highly visible user interfaces that enable people to communicate with programs to often invisible,
yet necessary, hardware interfaces that connect devices and components inside the
computer.
- interpret
- To decode and execute a statement or an instruction. The term usually refers to executing a
program by decoding a statement, executing it, decoding the next statement, executing it, and so
on. In contrast, compilation involves decoding all statements into executable code; executing that
code is a separate step.
- isometric view
- In computer graphics, a display method that shows three-dimensional objects with height
and width but without the change in perspective that would be added by depth. A drawing
program that produces an isometric view of a cube, for example, shows the sides in relation to one
another, each side evenly proportioned with height and width but no depth; the sides thus do not
appear to grow smaller with distance as they do when the cube is drawn in perspective. An
advantage of the isometric view is that every edge in a three-dimensional drawing always has the
correct length for the scale of the drawing.
- link
- To produce an executable program from compiled modules (programs, routines, libraries)
by merging the object code (assembly language object code, executable machine code, or a
variation of machine code) of the program and resolving interconnecting references (such as a
library routine called by a program). Also, to connect two elements in a data structure by using
index variables or pointer variables.
- machine code
- The ultimate result of the compilation of assembly language or any high-level language such
as C or Pascal: sequences of 1's and 0's that are loaded and executed by a microprocessor.
Machine code, also known as machine language, is the only language computers "understand;" all
other programming languages represent ways of structuring human language so that humans can
get computers to perform specific tasks. A compiler translates programs encoded in a high-level
language into machine code.
- modular programming
- An approach to programming in which the program is broken into several independently
compiled modules. Each module exports specified elements (constants, data types, variables,
functions, procedures); all other elements remain private to the module. Other modules can use
only the exported elements. Modules clarify and regularize the interfaces among the major parts of
a program. Thus, they facilitate group programming efforts and promote reliable programming
practices. Modular programming is a precursor of object-oriented programming.
- NOT
- An operator that performs Boolean (or logical) negation. In Boolean terms, NOT TRUE = FALSE and NOT FALSE = TRUE. In logical terms, if value, for example, contains a binary value, NOT value changes each 0 bit in value to 1 and each 1 bit in value to 0.
- object code
- The code, generated by a compiler or an assembler, that was translated from the source code
of a program. The term most commonly refers to machine code that can be directly executed by the
system's central processing unit, but it can also be assembly language source code or a variation of
machine code.
- operation code = opcode
- The portion of a machine language or assembly language instruction that specifies the type of
the instruction (that is, what sort of operation the instruction performs) and the structure of the data
on which it operates.
- operand
- The object of a mathematical operation or a computer instruction. An operand can be data or
it can be the location (in memory or on disk) at which data is stored. For example, in the arithmetic
operation 2 + 3, the numbers 2 and 3 are data that represent the operands
of the add operation. However, in an assembly language instruction of the form MOVE
(to)A,(from)B, the operands A and B can represent two memory locations
that, in turn, hold data the MOVE instruction will transfer — from location B to location A.
- OR
- A logical operation for combining two bits (0, 1) or two Boolean values (false, true); if one or both values are 1 (true), it returns the value 1 (true). The possible combinations are shown in the following truth table:
- truth table
- A table showing the possible outcomes of a Boolean expression; the Boolean equivalent of a
multiplication table (AND, exclusive OR, NOT, OR).
- word
- The native unit of storage on a particular machine. Depending on the microprocessor, a
word can be an 8-bit, a 16-bit, or a 32-bit quantity.
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Miriam Claude Meijer, Ph.D.
03/01/05