Barrons Publishing Dictionary of Computer and Internet Terms 10th

CMS

1. (Conversational Monitor System) the interactive part of IBM’s VM/SP (VM/ESA) operating system for mainframe computers.

The key idea behind VM and CMS is that each user has a whole simulated mainframe computer all to himself. The simulated computer has a virtual disk (i.e., one large real disk file that simulates the function of a disk drive on which many small files can be stored). See also VIRTUAL MACHINE; VM/ESA.

2. Content Management System, software allowing an organization to manage the creation, publication, and updating of a set of web pages and other documents that have multiple authors. The system should ensure consistency (so that the web version of a document has the same content as the paper version); it should make sure that changes are only made to the most recent version (so different authors aren’t making changes to different versions of the document) and it must protect the documents against any changes made by unauthorized persons. Also, authors must use LOGICAL DESIGN when creating their documents so that the actual visual appearance can be determined at the time of publication.

CMYK the four standard printing inks: cyan, magenta, yellow, and black. When combined, these four colors can reproduce a full-color image. If you ask your computer to make color separations for a PROCESS COLOR job, four COLOR SEPARATIONS will be generated, one for each of the standard inks. See also SPOT COLOR.

(You may be wondering why K is used to stand for black instead of B. It’s to avoid confusion with cyan, which is a greenish blue, and could also lay claim to B.)

coaster (slang) a compact disc (CD) given away free as advertising material; if you don’t need the software, you can at least put the disc under your coffee cup.

coaxial cable a cable that consists of a single conductor surrounded by insulation and a conductive shield. The shield prevents the cable from picking up or emitting electrical noise. (Contrast TWISTED PAIR.) Coaxial cables are rated for their impedance, given in ohms, which indicates how the inductance and capacitance of the cable interact. For instance, RG58 cable is rated at 52 ohms. This impedance cannot be measured with an ohmmeter.

COBOL (Common Business-Oriented Language) a programming language for business data processing, developed in the early 1960s by several computer manufacturers and the U.S. Department of Defense. As the sample program in Figure 60 shows, COBOL statements resemble English sentences, and the structure of the program requires that some documentation be included. COBOL programs are long and wordy, but easy to read, making it easy for programmers other than the author to make corrections or changes.

IDENTIFICATION DIVISION.

PROGRAM-ID. COBOL-DEMO.

AUTHOR. M. A. COVINGTON.

ENVIRONMENT DIVISION.

CONFIGURATION SECTION.

SOURCE-COMPUTER. IBM-PC.

OBJECT-COMPUTER. IBM-PC.

DATA DIVISION.

WORKING-STORAGE SECTION.

77 SUM PICTURE IS S999999, USAGE IS COMPUTATIONAL.

77 X PICTURE IS S999999, USAGE IS COMPUTATIONAL. PROCEDURE DIVISION.

START-UP.

MOVE 0 TO SUM.

GET-A-NUMBER.

DISPLAY ”TYPE A NUMBER:” UPON CONSOLE.

ACCEPT X FROM CONSOLE.

IF X IS EQUAL TO 0 GO TO FINISH.

ADD X TO SUM.

GO TO GET-A-NUMBER.

FINISH.

DISPLAY SUM UPON CONSOLE.

STOP RUN.

FIGURE 60. COBOL program

Cocoa application (on the Macintosh) a software package written specifically for Mac OS X. Contrast CARBON APPLICATION.

code

1. a way of encrypting information (making it unreadable). See

ENCRYPTION.

2.a way of representing information on a machine or in some physical form. For example, the bit patterns in memory can be used as a code to stand for letters and digits.

3.computer programs, whether written in machine language (OBJECT CODE) or a programming language (SOURCE CODE).

code base the collection of computer program SOURCE CODE that constitutes a software product. For example, the code base of Windows Vista is derived from that of Windows NT.

code page the table of information, inside DOS and its derivatives, that tells it how to display characters and interpret keystrokes. Code pages other than the usual (default) one are normally used outside the United States to accommodate the characters needed for foreign languages.

code signing attaching a DIGITAL SIGNATURE to a piece of code so a person who downloads it will know its origin. If the code comes from a trusted person or organization, the user will be more likely to grant it permission to take a wider range of actions, such as writing to the local disk drive.

codec (coder-decoder or compressor-decompressor)

1.a software component that enables a computer to play and/or record a particular audio or video file format. A common problem is that not all PCs have codecs for all popular file formats, and since codecs are usually installed with software rather than as separate items, the user does not know what is and is not present. Occasionally, a slightly corrupted audio or video file will play successfully with one codec but not with another that should also handle it.

2.an electronic circuit for converting audio or video signals into or out of digital form.

coding the process of writing an algorithm or other problem-solving procedure in a computer programming language.

cognitive computing the use of computers in COGNITIVE SCIENCE.

cognitive engineering the practical application of COGNITIVE SCIENCE, especially as it involves computers; the art of building tools to help people think. Cognitive engineering is broader than ARTIFICIAL INTELLIGENCE because its goal is to build tools, not just models.

cognitive prosthesis a tool that extends the human mind, such as a calculator or computer.

cognitive science the scientific study of intelligence (as distinct from the study of the brain), including artificial intelligence and some branches of computer science. See ARTIFICIAL INTELLIGENCE.

cold boot, cold start see BOOT.

collate to place printed pages in order before they are bound into a book. Some photocopiers have the ability to collate multipage documents automatically.

When printing multiple copies of a document, choose “collate” if you want the pages printed in the correct order and you don’t mind taking some extra time; the whole document will be sent to the printer more than once. If you do not choose “collate,” you will get all the copies of page 1, followed by all those of page 2, and so on; printing will be faster because the printer will receive each page only once, followed by a command to print it repeatedly.

collating sequence the alphabetical order of all characters representable on a computer (including digits, punctuation marks, and other special characters). The collating sequence is important because it is often necessary to sort (alphabetize) data that includes characters other than letters. The collating sequence of a computer is the same as the order of the numeric codes for the characters. See ASCII; EBCDIC.

collector one of the three layers of a bipolar transistor. See TRANSISTOR.

collision the situation in which two computers are trying to transmit on the same Ethernet network segment at the same time. Each of them will try

again after a random length of time (not the same length of time, or they would collide again, ad infinitum). Some collisions are normal on any busy network. Constant collisions indicate that the network is overloaded. See ETHERNET.

FIGURE 61. Additive color mixing

color the visible difference between different wavelengths of light. Fortunately, the human eye can be fooled—the color of any wavelength can be simulated by mixing light of other wavelengths. Colors on a CRT screen are produced by mixing red, green, and blue light from tiny phosphor dots. Colors on paper are produced by mixing or alternating inks in various ways.

Screen colors are specified as RGB (red, green, and blue) values in either of two ways. One way is to define a PALETTE (a working set of colors) and assign numbers to the colors on it. For example, a bitmap image with 4 bits per pixel can distinguish up to 16 colors. The other way is to give values of red, green, and blue for each pixel. For example, 24-bit color uses 8 bits each for red, green, and blue, requiring a total of 24 bits per pixel.

Since 8 bits are used for each color, there are 28 = 256 different levels for that color. Each color value is often represented as two HEXADECIMAL digits, where 00 is the minimum value and FF is the maximum value. Here are some specific examples:

In general, if the red, green, and blue values are equal, the result will be a shade of gray.

Colors on paper are usually specified as CMYK (cyan, magenta, yellow, and black) or HSB (hue, saturation, and brightness). Because the pigments being mixed are completely different from the phosphor dots on the screen, printed colors do not always match screen displays, even after extensive CALIBRATION.

color channel a representation of color information in a color bitmap image. An RGB image has three channels: red, green, and blue. Each channel can be manipulated separately from the others.

color separations camera-ready artwork that has been broken down into individual printouts, one for each color of ink that is to be printed. All the elements that should print in black will be on one sheet, and all the elements that should print in red will be on another, and so forth. Each printout will have registration marks so that the colors can be aligned properly or registered (see REGISTRATION, definition 2).

color temperature a method of measuring the redness or blueness of a photographic light source by comparing it to the temperature (in degrees Kelvin) of a white-hot object that would produce the same color of light. Sunlight has a color temperature of about 5000 K; incandescent light bulbs, 2700 K to 3400 K. Color temperature measures only redness or blueness and does not account for other tints that a light source might have, such as green or purple.

color/gray map a paint program filter that allows adjustment of a picture’s color balance. In grayscale mode, it can be used to adjust the exposure of an imperfect black-and-white photo.

column move the operation of moving material to the left or right within a file (e.g., moving the material in columns 10–20 into columns 5–15 on several consecutive lines in one step). See EDITOR.

.com

1.a suffix indicating that a web or e-mail address belongs to a commercial entity (in any country, but mostly the United States). Along with .edu,

.gov, .int, .net, .org, and .mil, this is one of the original set of Internet toplevel domains. Since 2000, .com, .net, and .org have been assigned almost indiscriminately to organizations of all types. See also TLD; ICANN.

2.the filename extension used for small, nonrelocatable machine language programs in DOS. To execute the program, type the name of the file without the final “.COM”; for example, to execute AAA.COM, type aaa. Contrast EXE FILE.

COM (Component Object Model) Microsoft’s architecture for building software components (i.e., packages of procedures and data structures ready for use by programmers). Many of these components are referred to as ActiveX controls (see ACTIVEX).

Compaq a major manufacturer of IBM PC-compatible computers. Compaq’s first product, released in 1983, was the first PC CLONE (i.e., the first PC-compatible computer not made by IBM). In 1988 Compaq led a group of other computer companies in the development of a 32-bit PC bus (see EISA). In 1998, Compaq acquired Digital Equipment Corporation, manufacturers of the Alpha microprocessor. In 2002, Compaq merged with Hewlett-Packard.

compatibility mode the ability of recent versions of Microsoft Windows to simulate earlier versions in order to run older software. To set the compatibility mode for a piece of software, right-click on its icon and look for the settings under Properties.

compatible

1.able to work together. For example, a particular brand of printer is compatible with a particular computer to which it can be connected.

2.able to run the same software. See PC COMPATIBILITY.

compile-time error an error in a computer program that is caught in the process of compiling the program. For example, a compile-time error occurs if the syntax of the language has been violated. Contrast RUNTIME ERROR. See also BUG.

compiler a computer program that translates C, C++, BASIC, Pascal, or a similar high-level programming language into machine language. The high-level language program fed into the compiler is called the source program; the generated machine language program is the object program.

complement

1.either of two ways of representing negative numbers in binary:

a.The 1-complement of a binary number is obtained by simply changing every 0 to 1 and every 1 to 0. For example, the 1-com- plement of 0001 is 1110. In this system, 0000 and its complement 1111 both represent zero (you can think of them as +0 and –0, respectively).

b.The 2-complement of a binary number is found by reversing all the digits and then adding 1. For example, the 2-complement of 0001 is 1110 + 1 = 1111. This is the system normally used on most computers, and it has only one representation of zero (0000).

See BINARY SUBTRACTION.

2.the opposite of a color; the hue, which when mixed with the first hue, can give colorless gray. For example, red is the complement of green.

complex number a number consisting of two parts, called real and imaginary. Complex numbers are written in the form a + bi, where a is the real part, b is the size of the imaginary part, and i is the square root of –1. (If b = 0, the complex number is of course equal to a real number.)

Unlike real numbers, complex numbers can produce negative numbers when squared; because of this fact, all polynomials have complex roots even though some of them lack real roots. Another use of complex num-

bers is to represent vectors in two-dimensional space; the imaginary number line is thought of as running perpendicular to the real number line.

Arithmetic on complex numbers obeys the ordinary laws of algebra, as follows:

(a + bi) + (c + di) = (a + c) + (b + d)i

(a + bi) – (c + di) = (a – c) + (b – d)i

(a + bi) × (c + di) = ac + adi + bci + bdi2 = (ac – bd) + (ad + bc)i

Complex numbers are provided as a data type in FORTRAN and C++, and in mathematical packages such as Maple, but not in most other programming languages. See also MANDELBROT SET.

complexity theory the mathematical study of the time (number of steps) and amount of memory needed to perform a computation.

Suppose a computer is going to process n items of input. The time complexity of the calculation may be any of the following:

•Constant or O(1) if the computation takes the same number of steps regardless of how many items are to be processed. An example is copying a disk with the DOS diskcopy command, which duplicates the entire disk regardless of how much of it is actually in use.

•Linear or O(n) if the number of steps is proportional to n. An example would be copying a set of n names and addresses from one file to another, or finding the sum of n numbers, or any program that contains only one loop.

•Polynomial or O(nk) if the number of steps is proportional to n raised to some constant power. For example, if the computation involves comparing each item of input with all of the other items, it will take n2 steps. Many sorting algorithms are O(n2). A program that contains k nested loops, each with a number of steps proportional to n, will take time proportional to nk.

•Exponential or O(kn) if the number of steps is proportional to some constant k raised to the nth power. This is what happens if the computer has to try arranging n elements in all possible sequences. Exponential-time computations are generally not practical.

There are some other possibilities; for example, Quicksort takes time proportional to n log n, which is less than n2.

In calculating complexity, we ignore factors that become insignificant as n becomes large. Suppose a computation requires n2 +3n +5 steps. For sufficiently large n, this gets closer and closer to n2, so we say that the complexity is O(n2).

Besides the time complexity, a computation may require constant, linear, polynomial, or exponential amounts of memory. See also COMPUTER SCIENCE; LIMITS OF COMPUTER POWER; QUICKSORT.

component any part of a larger system, either software or hardware. Reusable parts of programs are called software components. For examples of how software components are used, see ACTIVEX; COM; CORBA.

composite video the kind of video signal used in an analog TV set. The whole signal is transmitted on one wire. By contrast, an RGB signal has separate wires for red, green, and blue. See MONITOR.

compositing the combining of bitmap images from different sources or different objects in a single image. The opacity, or ALPHA, of each object determines how it combines with objects behind it. See also CHROMA-KEYING.

compression see DATA COMPRESSION.

CompuServe an online information service based in Columbus, Ohio, accessible by modem from anywhere in the United States. (See MODEM.) Since 1998, CompuServe has been a subsidiary of AOL. For further information, see www.compuserve.com.

computational linguistics the use of computers in the study of human language, and the study of how to make computers understand information expressed in human languages. See

PARSING.

computer a machine capable of executing instructions on data. The distinguishing feature of a computer is its ability to store its own instructions. This ability makes it possible for a computer to perform many operations without the need for a person to type in new instructions each time.

Computer a FOLDER on the DESKTOP of Microsoft Windows Vista that contains all the disk drives, the Control Panel, and other information about the system.

Ordinarily, folders are directories. The root directory of a disk drive is also a folder. “Computer” is a special folder that gives you access to the entire machine.

In previous versions of Windows, this folder was called “My Computer.”

computer architecture the design and internal structure of digital computers.

Fundamentally, a computer is a machine that can store instructions and execute them. Thus, it consists of two major parts, MEMORY and the central processing unit (CPU), which communicate through a set of parallel electrical connections called the BUS (Figure 64). The bus also connects to input-output devices such as a screen, a keyboard, and disk drives.

The CPU spends its time retrieving instructions from memory and doing whatever those instructions say. Each instruction is a pattern of bits (binary ones and zeroes, represented by electrical on and off signals). When the instruction reaches the CPU, the CPU must decode (recognize) it and activate the appropriate functional unit within the CPU in order to carry out the instruction. Functional units include adders, multipliers, circuits to compare bit patterns, etc., all of which are built from logic gates (for an example, see BINARY ADDITION).