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Barrons Publishing Dictionary of Computer and Internet Terms 10th

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application framework

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application framework a set of predefined procedures or classes that saves the programmer much of the work of writing a program with a sophisticated user interface. Using an application framework, the programmer need not write code to handle menu choices, mouse movements, etc., because that work has already been done.

An important early application framework was MacApp for the Macintosh. Newer programming languages such as Delphi, Visual Basic, and Java have application frameworks built in.

application program a computer program that performs useful work not related to the computer itself. Examples include WORD PROCESSORs, PRESENTATION GRAPHICS programs, DESKTOP PUBLISHING programs, SPREADSHEETs, DATABASE MANAGEMENT programs, CAD and CAM systems, and ACCOUNTING SYSTEMs. Contrast UTILITY; OPERATING SYSTEM.

applications programmer a person who writes programs that use the computer as a tool to solve particular problems, rather than just to manage the computer itself. Contrast SYSTEMS PROGRAMMER.

arc

1.part of a circle.

2.a data compression program for the IBM PC formerly produced by System Enhancement Associates in the mid-1980s, a precursor of ZIP.

See ZIP FILE.

arccos, arc cosine the inverse of the trigonometric cosine function. If x = cos y, then y = arccos x. Many computer languages provide the arc tangent function but not the arc cosine function. You can work around this by using the relation:

arccos x = arctan

1x2

x

 

where x is positive and angles are expressed in radians. See also

TRIGONOMETRIC FUNCTIONS.

archival storage storage for data that must be kept for a long time but will seldom be used, such as backup copies of working programs. Microcomputers often use CD-R, DVD-R, or external hard disks for archival storage. Magnetic tape is a traditional form of archival storage, but the tapes should be copied every 2 or 3 years if their contents are still needed, since tapes can become demagnetized with age. See also GRANDFATHER TAPE.

archive

1. a filing system for information designed to be kept for a long time.

See ARCHIVAL STORAGE.

2. a file containing the compressed contents of other files. The original files can be reconstructed from it. See ARC; ZIP FILE; TAR FILE; DATA COMPRESSION.

INTERNET; WIDE AREA NET-

27

arrange

3. in Windows, a file attribute that says whether or not the file has been backed up by copying to another disk or tape. The attrib command can be used to examine or change archive bits. The archive bit makes it possible to back up only the files that have not already been backed up. See

ATTRIBUTES.

arcsin, arc sine the inverse of the trigonometric sine function. If x = sin y, then y = arcsin x. Many computer languages provide the arc tangent function but not the arc sine function. You can work around this by using the relation:

x

arcsin x = arctan

1x2

in which all angles are expressed in radians. See TRIGONOMETRIC

FUNCTIONS.

arctan, arc tangent the inverse of the trigonometric tangent function. If x = tan y, then y = arctan x. In BASIC, the arc tangent function is called

ATN. See TRIGONOMETRIC FUNCTIONS.

arguments (actual parameters) values passed to a function or procedure by the calling program. See ACTUAL PARAMETER.

ARPANET a computer network originally developed for the U.S. Defense Advanced Research Projects Agency (ARPA, now known as DARPA) to link research institutions. ARPANET introduced the TCP/IP protocols and eventually developed into the Internet. See

WORK; TCP/IP; PROTOCOL.

arrange

1. to place the icons on the screen in neat rows and columns, retrieving any that have been moved off the edge of the screen (Figure 12).

In Windows, “Arrange Icons” is on the menu that pops up when you right-click on an empty area of the desktop; it is also on the “View” menu of individual windows.

If you want the computer to keep the icons arranged automatically, turn on the “Auto arrange” feature; a check mark shows that it is selected. See also CASCADE; TILE.

FIGURE 12. “Arrange Icons”

array

28

2. to place an item in relation to other items. In drawing programs, there is usually an Arrange menu that contains commands (ALIGN; SEND TO BACK; TO BACK; etc.) relating to the placement of selected objects. Objects are layered as if they were opaque pieces of paper.

array a collection of data items that are given a single name and distinguished by numbers (subscripts). For example, in C and related languages, the declaration

int x[5];

creates an array of five elements that can be referred to as x[0], x[1], x[2], x[3], and x[4]. (In some languages, such as BASIC, the elements are numbered from 1 rather than from 0.)

FIGURE 13. Array (one-dimensional)

You can store numbers in these elements with statements such as

x[0] = 10; x[1] = 43; x[2] = 8; x[3] = 91; x[4] = -5;

just as if each element were a separate variable. You can also perform input and output on array elements just as if they were ordinary variables.

Arrays are useful because they let you use arithmetic to decide which element to use at any particular moment. For example, you can find the total of the numbers in the five-element array x by executing the statements:

total = 0;

for (i=0; i<5; i++)

{

total = total + x[i];

}

Here total starts out as 0 and then gets each element of x added to it. Arrays can have more than one dimension. For example, the declara-

tion int y[3][5] creates a 3 × 5 array whose elements are:

y[0][0] y[0][1] y[0][2] y[0][3] y[0][4] y[1][0] y[1][1] y[1][2] y[1][3] y[1][4] y[2][0] y[2][1] y[2][2] y[2][3] y[2][4]

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artificial intelligence

Multidimensional arrays are useful for storing tables of data, such as three test grades for each of five students. See also DATA STRUCTURES; SORT.

FIGURE 14. Array (two-dimensional, 3 × 5)

arrow keys keys that move the cursor up, down, left, or right. The effect of these keys depends on the software being used. In a GUI environment, the arrow keys are basically an alternative to a mouse. Some drawing environments let you NUDGE the selected object with the arrow keys, giving you greater precision. Touch typists sometimes prefer the arrow keys to a mouse because it allows them to keep their hands on the keyboard.

See KEYBOARD; MOUSE; NUDGE.

artifact any unwanted part of a signal or image that results from the way it was recorded or processed. For instance, a low-level hiss is a familiar artifact of tape recording.

If you greatly increase the brightness or contrast of a JPEG image, you may see unusual stripes or blocks of color. They are artifacts of JPEG compression, in parts of the picture where the JPEG algorithm chose to sacrifice low-contrast detail in order to make the file smaller.

See JPEG.

artificial intelligence (AI) the use of computers to simulate human thinking. Artificial intelligence is concerned with building computer programs that can solve problems creatively, rather than just working through the steps of a solution designed by the programmer.

One of the main problems of AI is how to represent knowledge in the computer in a form that can be used rather than merely reproduced. In fact, some workers define AI as the construction of computer programs that utilize a knowledge base. A computer that gives the call number of a library book is not displaying artificial intelligence; it is merely echoing back what was put into it. Artificial intelligence would come into play if the computer used its knowledge base to make generalizations about the library’s holdings or construct bibliographies on selected subjects. See EXPERT SYSTEM.

Computer vision and robotics are important areas of AI. Although it is easy to take the image from a TV camera and store it in a computer’s memory, it is hard to devise ways to make the computer recognize the objects it “sees.” Likewise, there are many unsolved problems associated with getting robots to move about in three-dimensional space—to

ASC

30

walk, for instance, and to find and grasp objects—even though human beings do these things naturally.

AI also includes natural language processing—getting computers to understand speech, or at least typewritten input, in a language such as English. In the late 1950s it was expected that computers would soon be programmed to accept natural-language input, translate Russian into English, and the like. But human languages have proved to be more complex than was expected, and progress has been slow. See NATURAL LANGUAGE PROCESSING.

Do computers really think? Artificial intelligence theorist Alan Turing proposed a criterion that has since become known as the Turing test: A computer is manifesting human-like intelligence if a person communicating with it by teletype cannot distinguish it from a human being. Critics have pointed out that it makes little sense to build a machine whose purpose is to deceive its makers. Increasing numbers of AI workers are taking the position that computers are not artificial minds, but merely tools to assist the human mind, and that this is true no matter how closely they can be made to imitate human behavior. See also COGNITIVE ENGINEERING; COGNITIVE PROSTHESIS; COGNITIVE SCIENCE; COMPLEXITY THEORY; ELIZA; LIMITS OF COMPUTER POWER; NEURAL NETWORK; TURING TEST.

ASC the function, in BASIC, that finds the ASCII code number associated with a given character. (See ASCII.) For example, ASC(A) is 65 because the ASCII code of the character A is 65 (expressed in decimal).

ascender the part of a printed character that rises above the body of the letter. For instance, the letter d has an ascender and the letter o does not.

See DESCENDER; TYPEFACE; X-HEIGHT.

FIGURE 15. Ascenders

ASCII (American Standard Code for Information Interchange) a standard code for representing characters as numbers that is used on most microcomputers, computer terminals, and printers. In addition to printable characters, the ASCII code includes control characters to indicate carriage return, backspace, etc. Table 3 (page 31) shows all the ASCII character codes as decimal numbers. For two popular extensions of ASCII, see IBM PC (character set chart) and ANSI character set (Table 2, page 23). For alternatives to ASCII, see EBCDIC and UNICODE.

ASCII file a text file on a machine that uses the ASCII character set. (See TEXT FILE.) In Windows, each line ends with a carriage return and line feed (code 13 and 10).

31

ASCII graphics

TABLE 3

ASCII CHARACTER CODES (DECIMAL)

FIGURE 16. ASCII graphics

ASCII graphics an amusing technique of drawing pictures using only the standard keyboard characters (Figure 16). By making use of the intrinsic shapes of the characters, or of their relative densities, the artist can render surprisingly realistic graphics. These pictures are best when designed and displayed in a fixed-pitch font. (See FIXED-PITCH TYPE.)

ASSEMBLY LANGUAGE; MACHINE LANGUAGE;

ASIC

32

Because ASCII graphics uses only standard characters, these pictures can easily be transmitted by e-mail or in newsgroup postings and are popular in a SIGNATURE FILE.

ASIC (Application Specific Integrated Circuit) an integrated circuit (silicon chip) specifically made for a particular complete piece of electronic equipment. For example, the video controller in a typical PC is an ASIC designed specifically for use on that particular make and model of video card, whereas the memory chips are standard ICs also used in other types of computers.

Ask.com a search engine originally called “Ask Jeeves” that began in 1996 as a natural-language search engine able to understand English questions such as “what is a platypus?” In February 2005 it was reformed as a conventional search engine at Ask.com.

ASP

1.(Active Server Pages) on Windows web servers, a system for generating web pages partly or completely by computation, not by launching a separate program as in CGI, but by running scripts interpretively within the web pages as they are delivered to the client. Thus, a web page can be written partly in VBscript or another programming language in order to do computation as it is being served.

The current version of ASP, using the .NET Framework, is called ASP.NET. See IIS. Contrast CGI (definition 1); PHP.

2.(Application Service Provider) a network service provider that also provides application software, such as networked database programs.

Compare INTERNET SERVICE PROVIDER, CONTENT PROVIDER.

aspect ratio the ratio of height to width.

ASPI (Advanced SCSI Programming Interface) a standard way for application programs to access SCSI hardware. See SCSI.

assembler a computer program that translates assembly language into machine language. See

COMPILER.

assembly in Microsoft’s .NET Framework, a set of files containing software components that work together as a single program. All the components are explicitly and uniquely identified so that accidental substitutions cannot occur. (Assembly in this sense has nothing to do with assembly language.) See .NET FRAMEWORK. Contrast DLL HELL.

assembly language a computer language in which each statement corresponds to one of the binary instructions recognized by the CPU. Assembly-language programs are translated into machine code by an assembler.

Assembly languages are more cumbersome to use than regular (or high-level) programming languages, but they are much easier to use than

33

assignment statement

pure machine languages, which require that all instructions be written in binary code.

Complete computer programs are seldom written in assembly language. Instead, assembly language is used for short procedures that must run as fast as possible or must do special things to the computer hardware. For example, Figure 17 shows a short routine that takes a number, checks whether it is in the range 97 to 122 inclusive, and subtracts 32 if so, otherwise leaving the number unchanged. (That particular subtraction happens to convert all lowercase ASCII codes to their uppercase equivalents.)

This particular assembly language is for the Intel 8086 family of processors (which includes all PC-compatible computers); assembly languages for other processors are different. Everything after the semicolon in each line is a comment, ignored by the computer. Two lines (PROC and ENDP) are pseudo instructions; they tell the assembler how the program is organized. All the other lines translate directly into binary codes for the CPU.

Many of the most common operations in computer programming are hard to implement in assembly language. For example, there are no assembly language statements to open a file, print a number, or compute a square root. For these functions the programmer must write complicated routines from scratch, use services provided by the operating system, or call routines in a previously written library.

;Example of IBM PC assembly language

;Accepts a number in register AX;

;subtracts 32 if it is in the range 97-122;

;otherwise leaves it unchanged.

SUB32

PROC

 

; procedure begins

here

 

CMP

AX,97

; compare AX to

97

 

 

JL

DONE

; if less, jump

to

DONE

 

CMP

AX,122 ; compare AX to

122

 

JG

DONE

; if greater, jump to DONE

 

SUB

AX,32

; subtract 32 from AX

DONE:

RET

 

; return to main program

SUB32

ENDP

 

; procedure ends

here

FIGURE 17. Assembly language

assignment statement a statement in a computer language that calculates the value of an expression and stores that value in a variable. For example, this is an assignment statement in C:

y = sqrt(a*x*x + b*x + c);

This statement calculates the value of ax2 + bx + c and then gives that value to the variable y. Another example is

i = i + 1;

which makes i take on a value 1 greater than its previous value.

HAYES COMPATIBILITY.

associate

34

associate to tell a computer that a particular file should always be processed by a particular program, so that the next time the user opens the file, that program will automatically start.

Under Windows, associations are largely based on filename extensions. (See EXTENSION, definition 2.) To change the association of a file extension, open any directory (folder); then select View, Folder Options, File Types. Associations can also be changed by editing the REGISTRY.

asterisk the star-shaped character *. An asterisk is usually used to mark a footnote.

In Windows, UNIX, and other operating systems, an asterisk is used as a wild card character, to match any characters occurring in a particular place in a filename. For example, if you type dir *.exe at a command prompt, you will get a list of all files whose names end in exe. See WILD CARD.

FIGURE 18. Asterisks

asynchronous not synchronized. For example, most computer terminals use asynchronous data transmission, in which the terminal or the computer is free to transmit any number of characters at any time. The bits constituting each character are transmitted at a fixed rate, but the pauses between characters can be of any duration.

asynchronous discussion a discussion where the participants do not all have to be present at the same time. For example, in a newsgroup, participants can read comments about a particular topic that have been previously posted by other participants and then add to them. See

NEWSGROUP.

AT (Advanced Technology) the class of IBM PCs originally introduced in 1984 using the 80286 microprocessor and a 16-bit bus. See IBM PC.

Contrast XT.

AT command set the set of commands used to control Hayes modems; they all begin with the letters AT. See

at sign the symbol @, which stands for “at” and was originally used in price quotes (e.g., 4 items @ $3 each) and is now used in e-mail addresses (jones@somewhere.com). Some colorful nicknames for @ include “elephant’s ear” and “cinnamon bun.”

In Windows .bat files, commands beginning with @ are not displayed on the screen.

FIGURE 19. At sign

ARC TANGENT; TRIGONOMETRIC FUNCTIONS.

35

AUP

ATA (AT Attachment, where AT means PC AT) the interface used by IDE hard disks, essentially a buffered connection to the system bus. See also IDE.

ATA over Ethernet see AOE.

ATAPI (AT Attachment Packet Interface) the interface used by CD-ROM drives and other devices other than hard disks that are connected to an IDE hard disk controller.

Athlon a high-speed Pentium-compatible microprocessor made by AMD.

ATM

1.online abbreviation for “at the moment” (i.e., now).

2.in banking, abbreviation for automatic teller machine.

3.in networking, abbreviation for Asynchronous Transfer Mode, a set of high-speed data transmission protocols. See PROTOCOL. Contrast

IPX/SPX; NETBEUI; TCP/IP.

ATN the function, in BASIC, that computes the trigonometric arc tangent.

See

attachment a file transmitted as part of a piece of electronic mail. See ELECTRONIC MAIL.

atto- metric prefix meaning ÷1,000,000,000,000,000,000. Atto- is derived from the Danish word for “eighteen” (because it signifies 10–18). See

METRIC PREFIXES.

attributes the properties of files in Windows and similar operating systems. Files can be marked as hidden, system, read-only, and archive (which means that they have changed since last backed up to tape). The attrib command displays and changes file attributes.

auction a sale in which buyers make bids (offers) and the highest offer is accepted. For information about online auctions see EBAY. See also

DUTCH AUCTION; RESERVE PRICE; BID.

audio sound, represented by means of electronic signals. See also SOUND CARD; FM SYNTHESIS; WAVETABLE SYNTHESIS; MIDI. Contrast VIDEO.

FIGURE 20. Audio (sound) waveform displayed graphically

audit trail a record kept by a computer program that shows how data was entered into the computer. These records are essential for ensuring the reliability of financial data processing systems.

AUP see ACCEPTABLE-USE POLICY.

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