Barrons Publishing Dictionary of Computer and Internet Terms 10th

centi- metric prefix meaning ÷ 100. Centi- is derived from the Latin word for “hundredth.” See METRIC PREFIXES.

central processing unit see CPU.

Centrino a set of integrated circuits made by Intel comprising the PENTIUM M microprocessor and associated components designed for use in laptop computers with wireless networking.

Centronics interface a standard protocol for parallel data transmission to and from microcomputer equipment, especially printers. It was originally used on Centronics printers. The PARALLEL PORT of a microcomputer is normally Centronics-compatible. See also IEEE 1284; PROTOCOL.

The connector usually used with a Centronics interface is similar to one type of SCSI connector but has 36 connections instead of 50 (Figure 54).

FIGURE 54. Centronics interface connector

certainty factor see CONFIDENCE FACTOR.

certificate authority a trusted organization that issues digital certificates. (See CERTIFICATE, DIGITAL.) For examples, see www.verisign.com and www.thawte.com.

certificate, digital an attachment to an electronic message using public key encryption to verify that the message truly comes from the sender it claims to come from, and has not been altered in transit. To be useful, certificates must be issued by a trusted CERTIFICATE AUTHORITY so that the recipient can check on the public key. See ENCRYPTION.

Your operating system may warn you if you try to run software that was downloaded or e-mailed through the Internet and is not signed with a digital certificate. The digital certificate would help you be sure that the software has not been altered to insert a VIRUS or other MALWARE. This is important when you are downloading software from a third party, but not when you are sure you are downloading it directly from its originator. Nor does the certificate prove that the software is reliable or works correctly—it only verifies the identity of the author.

CGI

1. (computer-generated image) a method of ANIMATION in which the computer creates two-dimensional moving images of three-dimensional objects, replacing older animation techniques that involved a series of hand-drawn or hand-edited images.

2. (Common Gateway Interface) a standard way for computer programs to generate web pages as needed, containing current information or the results of computations. Instead of a file containing the web page itself, the server contains a program that writes the web page to standard output. This program is often called a CGI script. It can receive input from the web page that links to it, either through environment variables or on the standard input stream. See also PHP.

Note: The two definitions are easy to confuse, since animations on web pages can be generated by CGI programs (definition 1).

CGM (Computer Graphics Metafile) an ANSI standard file format for graphical data (both vector and bitmap). CGM files are used mainly for exchanging data between applications.

.ch suffix indicating that an e-mail or web address is registered in Switzerland (the Swiss Confederation, or in official Latin,

Confoederatio Helvetica). See TLD.

chad the small pieces of paper that have been punched out of a PUNCHED CARD or punched paper tape. Until the 2000 U.S. presidential election, most people had never heard of chad, but in that year, the failure of some voting machines to punch neat holes in cards may have changed the course of history.

chain letter a message that is intended to be forwarded from each recipient to as many others as possible. On the Internet, chain letters are very unwelcome because they waste money; the cost of delivering e-mail is borne by the recipient’s site. Many chain letters perpetrate hoaxes or pyramid schemes (see HOAX; PYRAMID SCHEME).

channel

1.a radio frequency or communication path (e.g., a TV channel).

2.a high-speed data communication device used to interface IBM mainframe computers with input-output devices.

3.in desktop publishing, a set of images that will compose the final image when combined. The most common use for channels is the representation of the CMYK color separations in a paint program. Each color has its own channel. Sometimes channels can be used like layers in a DRAW PROGRAM. Selected areas can be saved to a new channel, manipu-

lated separately from the rest of the image, and later recombined with the main channel.

4. a discussion forum in Internet Relay Chat or a similar service. See

IRC; CHAT ROOM.

5. a web page that is constantly updated, so that viewing it is like watching a television channel. See PUSH (definition 2).

character any symbol that can be stored and processed by a computer. For example, A, 3, and & are characters. The ASCII coding system is one way of representing characters on a computer. See ASCII; ANSI (definition 3); EBCDIC; UNICODE.

character set the set of characters that can be printed or displayed on a computer. For examples see ASCII; ANSI; EBCDIC; IBM PC; UNICODE.

character string a series of characters, such as ”JOHN SMITH” or ”R2D2.” See

STRING.

charge-coupled device see CCD IMAGE SENSOR.

chat room an electronic forum in which users can communicate with each other in real time. Chat rooms are found on the Internet (see IRC) and on online services such as CompuServe and AOL.

People in chat rooms use a lot of abbreviations so they can type as quickly as possible and to offer hints of their emotional reactions (see also EMOTICON). Many times the abbreviations are recognized from their context, but until you get the hang of it, a chat room can be a bewildering place. For example, the words two, too, and to are almost never written out—they are replaced by the numeral 2. The numeral 4 is used to replace four and for. See Table 5 for some common phrases. See also

ELECTRONIC MAIL; INSTANT MESSAGE; LEETSPEAK; SOCIAL NETWORKING.

check box a small box (in a window) that the user can turn on or off by clicking with the mouse. When on, it displays an X or check mark in a square; when off, the square is blank. Unlike option buttons, check boxes do not affect each other; any check box can be on or off independently of all the others.

Figure 55. Check Box

checked (describing Windows versions) containing extra error detection and debugging code. Checked versions of Windows are used only for certain kinds of development work. Contrast FREE.

checksum a number that accompanies data transferred from one place to another and helps to ensure that the data was transferred correctly.

One way to ensure correct transmission would be to transmit all of the information twice; if there were an error, the two copies would almost certainly disagree. However, this is too time-consuming to be practical. A better approach is to divide the information into small packets, such as lines of text or disk sectors, and compute a checksum for each packet. A checksum is a number that would almost certainly be different if the information were altered.

A simple way to compute a checksum is to add up the ASCII codes for all the characters of data (see ASCII) and take the result modulo 256.

Chicago the code name by which Windows 95 was identified before its release. Compare CAIRO; LONGHORN; MEMPHIS; WHISTLER; BLACKCOMB.

child an object created with the properties of another object (called the PARENT). Updating the properties of the parent object affects the children, but changing the properties of the child does not affect the parent. See

VECTOR GRAPHICS; OBJECT-ORIENTED PROGRAMMING.

child process a process launched by and considered dependent on another process. See PROCESS; MULTITASKING; UNIX.

chip see INTEGRATED CIRCUIT.

chipset a set of integrated circuits intended to be used together. For example, many modems use a chipset made by Rockwell, and many motherboards use an Intel chipset along with a Pentium processor.

chmod UNIX command for changing file permissions. For example of its use, see PERMISSION.

chroma-keying the process of digitally combining video images by the use of a subtractive background. This is the method used to show a weather forecaster in front of a set of maps. The person is videotaped in front of a blue or green background. The colored background is digitally removed (hence chroma-, meaning color), and the desired map is put in place of it. The weather forecaster watches a monitor off-camera so he or she can point to the correct spot.

Chroma-keying is also used for a variety of special effects in movies.

chromogenic print a picture printed photographically with colored dyes; a conventional color photograph or (much less often) a black-and-white photo produced with similar chemistry. Contrast GELATIN SILVER PRINT;

GICLÉE PRINT.

Church’s Thesis (or Church-Turing Thesis) the hypothesis that a TURING MACHINE (or any of its mathematical equivalents) is as powerful as a mechanical computing device can be; other devices are more efficient at particular tasks, but none of them can do anything fundamentally different. It was proposed, at different times and in different forms, by Alan Turing and by the logician Alonzo Church.

CIFS (Common Internet File System) the file sharing protocol that forms the basis of Microsoft Windows networking. Formerly known as SMB (Server Message Block), it is also supported by UNIX and Linux systems using the Samba software package. See SAMBA. Contrast NFS.

cinnamon bun (slang) the symbol @; see AT SIGN.

CIO Chief Information Officer, an officer of a business responsible for its computers and data processing.

CIPA (Children’s Internet Protection Act) a law passed by Congress in 2000 (47 USC 254) requiring libraries to use blocking programs to prevent

access to Internet sites with objectionable content. The Supreme Court upheld this law in 2003 (United States v. American Library Association).

circularity the problem that arises when a computer cannot finish a task until it has already finished it—an impossible situation. For example, in a spreadsheet, a circularity problem arises if you enter the formula 2*B1 into cell A1 and then enter the formula A1/2 into cell B1. In order to evaluate each of the cells the computer needs the value of the other one. Thus, it cannot proceed, and it displays a warning message instead. See Figure 56.

FIGURE 56. Circularity in a spreadsheet

circumflex the symbol ˆ, either written by itself as an ASCII character, or written above a letter (e.g., ê).

CISC (Complex Instruction Set Computer) a computer with many different machine language instructions. The IBM PC, 68000-based Macintosh, Pentium, IBM 370 mainframe, and VAX are CISC machines.

Contrast RISC.

Cisco Systems, Inc. a company headquartered in San Jose, California that is the leading provider of high-speed networking hardware. The web address is www.cisco.com.

class an object type in object-oriented programming. See OBJECT-ORIENTED PROGRAMMING.

Class A (describing computer equipment) approved by the U.S. Federal Communications Commission for use in industrial or business but not residential areas because of the risk of radio-frequency interference. See FCC (definition 1).

Class B (describing computer equipment) approved by the U.S. Federal Communications Commission for use in residential areas because the risk of radio-frequency interference is low. See FCC (definition 1).

class library a set of classes available to programmers in an object-oriented language such as Java or C++. In addition to the base classes that come with the language itself, a programmer can use and extend other classes created from other sources.

Classic mode an operating system mode which allows Macintosh computers running OS X to run older Mac OS 9 software.

clear

1.to set a flip-flop or memory location to zero.

2.to make the screen go blank.

click to press one mouse button very briefly (usually the leftmost button, if there is more than one). Contrast PRESS; DOUBLE-CLICK. See also WINDOW.

Figure 57. Click

click path analysis the study of the sequence of web pages reached by visitors to a web site, which can be helpful in determining if visitors can find information as was intended by the web designers.

clickable image a picture on a WEB PAGE or in a HYPERTEXT document that the user can select, by clicking with the mouse, in order to call up further information. See IMAGE MAP.

ClickOnce deployment a method of software installation, under Microsoft

.NET Framework, where a program is downloaded and installed from a web address and can automatically check the same web address for updated versions.

clickworker

1.a volunteer doing tedious computer work for scientific research, usually in short work sessions. For an example, see clickworkers.arc.nasa. gov/top.

2.(more generally) a worker who manages information with the aid of a computer, typically without being especially knowledgeable about or interested in computing.

client

1.a computer that receives services from another computer. For example, when you browse the World Wide Web, your computer is a client of the computer that hosts the web page.

2.an operating system component that enables a computer to access a particular kind of service. For example, computers that use Netware networks must have a Netware-compatible client installed.

client area the part of a window in which editing or drawing actually takes place. It does not include the borders, the title, the menu bar across the top, or the scroll bars, if any.

client-side application a computer program that runs on a network client rather than on the server. For instance, Java applets are client-side applications; when you view a web page that contains an applet, the applet is sent to your computer and runs on it. Contrast SERVER-SIDE APPLICATION.

clip art artwork that can be freely reproduced. Many of the pictures in newspaper advertisements come from clip art. Many clip art collections are available on diskettes or CD-ROMs for use with various drawing, painting, and desktop publishing programs.

FIGURE 58. Clip art examples

Clipboard on the Macintosh and in Windows, a holding area to which information can be copied in order to transfer it from one application program to another. For instance, the Clipboard can be used to transfer text from a word processor into a drawing program.

The contents of the Clipboard vanish when the computer is turned off. Also, in most software, only one item at a time can be on the Clipboard; the next CUT or COPY command will replace the old item with a new one.

See also PASTE.

clipping

1.(in Macintosh OS 9) a fragment of text or graphic image that can be temporarily stored on the Desktop. This provides another way (other than the Clipboard) for transferring information from one program to another.

2.in digital audio, chopping off the tops and bottoms of the sound waves, resulting in distorted sound.

clock

1. the circuit in a computer that generates a series of evenly spaced pulses. All the switching activity in the computer occurs while the clock is sending out a pulse. Between pulses the electronic devices in the computer are allowed to stabilize. A computer with a faster clock rate is able to perform more operations per second.

The clock speed of a computer is often given in megahertz (MHz) or gigahertz (GHz), where 1 MHz = 1,000,000 cycles per second and 1 GHz = 1000 MHz. Often, the clock speed is doubled or tripled inside the CPU so that high-speed signals do not have to be carried outside it. The original IBM PC had a clock speed of 4.77 MHz. See MICROPROCESSOR. 2. the circuit within a computer that keeps track of the date and time, often called a real-time clock or clock/calendar. Commonly, the realtime clock is powered by a battery and runs even when the computer is turned off.

clone

1.a computer that is an exact imitation of another (e.g., a clone of the IBM PC), or a software product that exactly imitates another. In biology, a clone is an organism that has exactly the same genetic material as another, such as a plant grown from a cutting.

2.in OBJECT-ORIENTED PROGRAMMING, to duplicate an object.

clone tool

1.a tool available in paint programs that allows you to duplicate areas. To use the clone tool, click on the center of the area you wish to copy. Move the cursor to where you want the new area to be. Press and hold down the mouse button (the leftmost button if there is more than one) while you paint in the image. The clone tool can be used to create a bunch of cherries out of a few, cover a gap left by deleting an area, or to put a third eye on someone’s forehead. It is not necessary to define the outline of an area or object when using the clone tool; it works from the center out as far as needed. See also RUBBER STAMP.

2.(in drawing programs) a tool that copies the properties of an object to a secondary object.

FIGURE 59. Clone tool

close

1. (in Windows) to exit a program and clear it from the computer’s memory. This is different from MINIMIZE in that a program reduced to an icon is still running and waiting for input from you, but a closed program has been put away. Most importantly, a minimized program is still being held in the computer’s memory. If you close a minimized program, you will regain the memory it is taking up.

2. (on the Macintosh) to reduce a window to an icon without quitting the application software. The Close button is at the far left of the title bar. Click once to close the open window. This sense of close is analogous to MINIMIZE in Windows. To clear the program from memory, choose Quit from the File menu.

This illustrates one of the most basic areas of confusion between Macintosh and Windows terminology. Be careful when talking to your cross-platform friends or you’ll both end up confused!

3.(in programming) to release a file when a program is finished using it.

4.(in electronics) to put a switch into the position that allows current to flow.

Closed Beta a test of incomplete software that is only open to a small group, such as the developer’s employees. See BETA TESTING.

cloud computing computing operations carried out over computers linked to the web. The users pay for computing as a service rather than pay for hardware purchases.

cluster

1.a group of disk sectors that are treated as a unit for purposes of allocating space; an ALLOCATION UNIT. See also LOST CLUSTER.

2.a group of servers that function as a single system.

cluster computing using networked computers to work on computationally complicated problems, often more economically than on a traditional SUPERCOMPUTER. Software needs to be designed to distribute the tasks to the different machines. For an example, see BEOWULF. The clustered computers are part of the same organization, in contrast with GRID COMPUTING.

CLV (constant linear velocity) in disk drives, a speed of rotation that varies depending on whether the drive is reading a long track near the edge of the disk or a short track near the center. Thus the disk itself passes beneath the head at a constant speed. Most CD-ROM drives use CLV.

Contrast CAV.

CMOS (complementary metal-oxide semiconductor) a type of integrated circuit noted for its extremely low power consumption and its vulnerability to damage from static electricity. CMOS devices are used in digital watches, pocket calculators, microprocessors, and computer memories. See FIELD-EFFECT TRANSISTOR.

CMOS image sensor an image sensor similar to a CCD, but that uses metal-oxide semiconductor (MOS) transistors for lower power consumption. See CCD IMAGE SENSOR; FOVEON.

CMOS RAM a special kind of low-power memory that stores information about the configuration of a computer. It is operated by a battery so that it does not go blank when the machine is turned off. Compare NVRAM.