Barrons Publishing Dictionary of Computer and Internet Terms 10th

2. a way of representing the main points of a text without giving all the details. People have been making outlines on paper for centuries, but a computer can simplify the process in two ways. First, with a word processor, it is easy to create a document by first typing an outline of it, and then going back and filling in the sections one by one. Second, software has been developed to let you display just the desired parts of an outline while concealing the rest. While you are working on one section, the details of other sections, even if they have already been written, can be removed from the screen.

FIGURE 186. Outline (definition 2)

Outlook popular e-mail and calendar software provided as part of the Microsoft Office suite.

Outlook Express the e-mail software provided with Microsoft Windows and also made available by Microsoft for other operating systems. A more elaborate commercial version is called Outlook.

output the information that a computer generates as a result of its calculations. Computer output may be either printed on paper, displayed on a monitor screen, or stored on disk or tape.

output device a device that shows, prints, or presents the results of a computer’s work. Examples of output devices include MONITORs, PRINTERs, and IMAGESETTERs.

overclocking the practice of running a CPU at higher than its rated clock speed. For example, a 2.2-GHz CPU might run successfully at 2.4 GHz.

Overclocking usually yields a small increase in performance and a substantial decrease in reliability. Overclocked CPUs emit more heat, requiring a larger HEAT SINK than when run at their rated speed.

Sometimes, physically identical CPUs are sold with different speed ratings because the manufacturer does not want to make separate types. In this case, the lower-rated ones are less expensive but can be overclocked with no risk of problems.

overflow the error condition that arises when the result of a calculation is a number too big to be represented in the available space. For example, adding 65,535 + 1 will cause an overflow on a computer that uses 16-bit unsigned integers, because 216 – 1 = 65, 535 is the largest integer repre-

sentable in that format. (Or, worse, if the computer does not detect overflows, it may simply compute 65, 535 + 1 = 0 without letting you know anything is wrong.) Compare UNDERFLOW.

overlaid windows windows that can overlap; when they do, one window hides the parts of others that are behind it (Figure 187). To bring another window to the front, move the mouse pointer into it and click the button.

Contrast TILED WINDOWS. See also CASCADE.

FIGURE 187. Overlaid windows

overwrite to write over information that is already on a disk. For example, if you copy a file called ABC.TXT onto a disk that already has a file with the same name, some operating systems will ask you whether you want to overwrite the old file. If you say no, the new file will not be copied.

own (slang) to conquer or defeat an opponent in a game; to break into a computer and control it.

P

P (on a digital camera) programmed autoexposure, a mode in which the camera chooses both the lens aperture and the shutter speed. Contrast A;

AV; S; TV.

p-p (peak-to-peak) a way of measuring AC voltage. See PEAK-TO-PEAK.

P2P

1.abbreviation for PEER-TO-PEER.

2.the use of peer-to-peer networking to share files over the Internet.

packet a group of consecutive characters sent from one computer to another over a network. On most networks, all communications are in the form of packets that begin with labels indicating the machine to which they are addressed.

packet radio the transmission of data (in packets) by radio. It is a fastgrowing hobby among radio amateurs (“hams”) and also has commercial applications as a way of linking computers without wires.

A typical amateur packet system consists of a computer linked by a terminal-node controller (TNC) to a VHF radio transmitter and receiver. The TNC constructs and recognizes packets. The packet radio protocol effectively prevents two systems from transmitting at the same time, and all data are error-checked. Packet systems are often used to run bulletin boards (see BBS). Unlike telephone-line BBSs, packet BBSs are inherently multi-user systems because each packet contains a label indicating its sender and receiver. Thus, the computer can keep track of many users concurrently.

Commercial packet systems often involve portable computer terminals carried by delivery or service personnel. The terminals are linked by radio to a main computer many miles away. See also AX.25; PROTOCOL.

page

1. information available on the World Wide Web. See

PAGE.

2. a section of memory that is accessible at one time. See VIRTUAL MEMORY.

page fault the situation that arises when the computer needs to access an area of memory that has been swapped out to disk; it is not a malfunction. See VIRTUAL MEMORY.

page frame an indication of the edges of the paper displayed by your computer’s software. The area around the page frame is called the pasteboard.

page layout software software specially designed for creating CAMERAREADY COPY. Page layout programs, such as Adobe InDesign and QuarkXPress, allow the desktop publisher to combine many separate

files of different types into a specified design. These special designs, called TEMPLATEs or STYLESHEETs, provide a framework to put the individual elements into. Most programs come with a library of predefined stylesheets.

Page layout software also allows more control over typography than most word processors. See

page printer a printer that forms, in its digital memory, a graphical image of the whole page, or requires the computer to do so, before printing it out. Laser printers are page printers, and inkjet printers commonly operate as page printers. Contrast LINE PRINTER.

pagination to divide a document into pages for printing.

paint program one type of program for drawing pictures on a personal computer. The user draws with the mouse pointer (or a graphics tablet), and commands are provided for drawing circles, lines, rectangles, and other shapes, as well as for drawing freehand and choosing colors.

Paint programs treat the picture as a grid of pixels (see PIXEL; BITMAP). Shadings are easy to produce by manipulating the color of each individual pixel. It is hard to move an element of the picture if it is not where you want it. Contrast DRAW PROGRAM.

More sophisticated paint programs are called photopaint programs because of their ability to retouch photographs and produce realistic images. See PHOTOPAINT PROGRAM.

PAL (Phase-Alternate-Line) the type of analog color TV signal used in Great Britain and many other countries, now being displaced by digital television. The screen consists of 625 lines, interlaced, and a complete scan takes 1/25 second. Color information is modulated on a 4.43-MHz subcarrier. Contrast DIGITAL TELEVISION; HDTV; NTSC; SECAM.

palette

1.a set of colors chosen from a much larger set. The whole set of displayable colors is also sometimes called a palette.

2.a floating window containing specialized tools or setting controls.

Palm a line of handheld computers and organizers, beginning with the pioneering Palm Pilot in 1996. Palm, Inc. is located in Milpitas, California; web address: www.palm.com.

palmtop a computer that you can hold in one hand while using it. Compare

PDA.

pan (animation and 3-D software) to move the viewing area left or right to see additional sections of the scene.

Pantone Matching System (PMS) a color matching and calibration system designed by the Pantone company. (Web address: www.pantone.com.) There are a wide variety of products all keyed to the same numbering system. If you want a certain color, you can specify it by its Pantone number

give notes, comments, or a translation into another language. Many Canadian documents are printed in parallel columns of English and French. Contrast NEWSPAPER COLUMNS.

parallel port an output device that lets a computer transmit data to another device using parallel transmission—that is, several bits sent simultaneously over separate wires. Traditionally microcomputers have used parallel ports to communicate with printers. See IEEE 1284.

FIGURE 188. Parallel circuit (two resistors)

FIGURE 189. Parallel port (with symbol indicating a printer)

parallel printer a printer that connects to a computer’s parallel port (rather than, for example, to a USB port or a network cable).

parallel processing computation carried out at the same time on different CPUs, or on a CPU that can execute more than one instruction at the exact same time.

By contrast, most multitasking is accomplished by making a single CPU switch its attention among several tasks. This is called concurrent processing or timesharing.

parameter a symbol that will be replaced in a procedure, function, or method by supplied values when the procedure is called. For example, if max is a function, then in max(x,y), x and y are the parameters. See

ACTUAL PARAMETER; FORMAL PARAMETER.

parens (slang) parentheses.

parent an object that gives its properties to a newly created object (the CHILD). Updating the properties of the parent object affect the children, but changing the properties of the child do not affect the parent.

See DRAW PROGRAM; INHERITANCE; OBJECT-ORIENTED PROGRAMMING.

parent directory the directory that contains another directory.

parental controls software options enabling parents to control what web sites their children access. See FILTER (definition 3).

parentheses the characters ( ), also called round brackets.

Usage note: The singular is parenthesis. That is, ( is a left parenthesis, ) is a right parenthesis, and () is a pair of parentheses. For use, see PRECEDENCE. Contrast ANGLE BRACKETS; CURLY BRACKETS; SQUARE BRACKETS.

programming languages. (See COMPILER; INTERPRETER.) Programs that accept natural-language input have to parse sentences in human languages.

Parsing is done by comparing the string to be parsed to a grammar, which defines possible structures. For example, Figure 190 shows the structure of the sentence “The dog chased the black cat.” Figure 191 shows a small part of the grammar of English.

Parsing can be done either top-down or bottom-up. In top-down parsing, the computer starts by looking for a particular constituent. It consults the grammar to determine what this constituent consists of, and then looks for those constituents instead, thus:

Look for Sentence

Rule 1: Sentence consists of Noun Phrase + Verb Phrase Look for Noun Phrase

Rule 2: Noun Phrase consists of Determiner + Noun Look for Determiner

Accept Determiner the from input string Look for Noun

Accept Noun dog from input string Look for Verb Phrase (etc.)

The process is complete when the input string is empty and all of the elements of a sentence have been found.

In bottom-up parsing, the computer accepts elements from the input string and tries to put them together, thus:

Accept the, which is a Determiner

Accept dog, which is a Noun

Determiner + Noun make a Noun Phrase

Accept chased, which is a Verb

Accept the, which is a Determiner

Accept black, which is an Adjective

Accept cat, which is a Noun

Determiner + Adjective + Noun make a Noun Phrase

Verb + Noun Phrase make a Verb Phrase

Noun Phrase + Verb Phrase make a Sentence

Parsing algorithms must be able to backtrack (back up and try alternatives) because the grammar provides alternatives. For example, a noun phrase may or may not contain an adjective, and a word like leaves can be a verb or a noun. Further, parsing algorithms usually use recursion to handle the recursive structure of human languages. For example, a noun phrase can contain a noun phrase, which can contain another noun phrase, as in the discoverer of the solution to the problem. See BACKTRACKING; NATURAL LANGUAGE PROCESSING; RECURSION.

Part 15 device a radio transmitter that is allowed to operate without a license under the terms of Part 15 of the Federal Communications Commission’s regulations (known to lawyers as 47 CFR 15). Examples

include cordless telephones, wireless intercoms, and some kinds of wireless computer communication devices (wireless LANs). Because individual Part 15 transmitters are not licensed, there is no way to guarantee that they will not interfere with each other, but spread-spectrum technology makes interference unlikely. By contrast, licensed transmitters can be given exclusive use of a particular frequency in a particular area.

See also SPREAD-SPECTRUM.

partition a part of a HARD DISK that is treated by the computer as if it were a separate disk drive. Most hard disks consist of only one partition, but multiple partitions are sometimes used with larger drives.

Pascal a programming language developed by Niklaus Wirth in the early 1970s. Pascal is essentially a modernized version of ALGOL, and it has greatly influenced the design of other languages, as well as becoming popular in its own right. See TURBO PASCAL for information on a popular version.

Figure 192 shows a sample program in Pascal. A Pascal program consists of:

•A PROGRAM statement to give the program a name (and, in older versions, to declare input and output files);

•Declarations of global variables;

•Declarations of procedures and functions;

•The keyword BEGIN, the action part of the main program, the keyword END, and finally a period to mark the end.

Procedures and functions, in turn, can contain their own declarations, including more procedures and functions (a kind of nesting that is not permitted in C).

Pascal is not case-sensitive (e.g., X and x are equivalent). In this book, uppercase letters are used for reserved words (keywords that cannot be redefined, such as IF, THEN, and ELSE), and lowercase letters for everything else.

Semicolons are used as separators between statements. Thus a statement ends with a semicolon only when what follows is the beginning of another statement. This contrasts with C and PL/I, which end every statement with a semicolon regardless of the context.

Comments in Pascal are enclosed in braces, {}, or the symbols (**). A statement does not have to fit on one line; lines can be broken anywhere that blank space is permitted.

Pascal provides four standard data types: real, integer, Boolean, and character. Integer variables can take on only values that are whole numbers or the negatives of whole numbers. Real variables can take on numerical values that include fractional parts, such as 23.432. Boolean variables are logic variables that can have only two possible values: true or false. Char variables can take on single character values.

An assignment statement in Pascal looks like this:

x := 3;