Barrons Publishing Dictionary of Computer and Internet Terms 10th

This statement gives the value 3 to the variable x. Note that the symbol for assignment is :=, not =. The arithmetic operators are + for addition,

– for subtraction, * for multiplication, / for floating-point division, div for integer division, and mod for modulo (remainder from division).

See also MODULA-2.

BEGIN REPEAT

write(’Enter a whole number (type 0 to quit): ’); readln(n);

status := ’ is prime’;

IF n>2 THEN continue := TRUE ELSE continue := FALSE;

i := 1;

max := TRUNC(SQRT(n));

{max is the largest divisor that must be checked to see if n is prime}

WHILE continue DO BEGIN

i:=i + 1;

IF (n MOD i)=0 THEN BEGIN

status := ’ is not prime’; continue := FALSE

END;

continue := (i < max); END; {end of WHILE loop}

write(n);

writeln(status); UNTIL n=0

END.

FIGURE 192. Pascal program

Pascal notation a way of combining words by running them together, all capitalized; ThisIsAnExample. Procedure names in Pascal programs are often formed this way. Contrast CAMEL NOTATION. See INTERCAPS.

Pascal, Blaise (1623–1662) a French mathematician who, in 1642, built a mechanical adding machine that was one of the early forerunners of calculators and computers.

passive FTP a variation on FTP (file transfer protocol) in which all connections are initiated by the client (the user’s PC), not the server. This is necessary because some routers and firewalls, for security reasons, do not allow the server to initiate connections to the client. In that situation, a user can establish an FTP connection but cannot get a list of files and folders. Passive FTP overcomes the problem.

To select passive FTP, type the command passive in a command-line FTP session, or make the appropriate choice in setting up your FTP client software. For example, in Microsoft Internet Explorer, passive FTP is an option under Tools, Internet Options, Advanced.

passive matrix an older type of liquid crystal display that produces lower contrast than newer ACTIVE MATRIX displays.

password a secret sequence of typed characters that is required to use a computer system, thus preventing unauthorized persons from gaining access to the computer.

If you are using a password to protect your computer:

•Protect your password. Keep it a secret and don’t share it.

•Don’t choose an obvious password. Use some imagination and forethought. What would be hard to guess? Your password is not your mantra and should not express your personality or indicate in any way who you are.

•Don’t use a word in any language; some people crack computers by automatically trying every word in a dictionary. Include digits and special characters to make your password hard to guess. See DIC-

TIONARY ATTACK.

•Use the initial letters of a memorable phrase or title to create a password. Again, using digits and special characters will help safeguard your password.

•Change your password regularly, but not so often you can’t keep track of it.

•When you need to provide passwords for multiple systems, distinguish between systems that need high security and those that can tolerate low security. Use a high security unique password for systems that provide access to your valuable personal data such as your e-mail account. When you need to give a password to obtain access to web information where security is not a crucial concern, use the same password for all of these locations (as long as it is different from your high-security passwords). This way you won’t have to keep track of a dozen different passwords for a dozen different organizations.

paste to transfer material from a holding area into the document you are editing. In Windows and Macintosh environments, the keyboard shortcut for paste is Ctrl-V. See CLIPBOARD; COPY; CUT.

PATA (parallel ATA) the original hardware implementation of the ATA hard disk interface, using parallel data transmission through a rectangular 40-pin connector, later expanded to 80 conductors by using the two sides of each hole separately. If no other type of interface is specified, “ATA” usually means PATA. See ATA. Compare ESATA; SATA.

patch to correct a defective piece of software by modifying one or more of the files on which it resides, rather than by installing a complete, corrected copy.

patent legal protection for the design of a machine or mechanical process, preventing others from using the same idea without the inventor’s permission. Unlike a copyright, a patent protects an idea itself, not just an expression of the idea. In the United States, a patent remains in force for 20 years.

Computer programs were not originally considered patentable, since they were viewed as mathematical discoveries. In recent years, however, software patents have become common, on the ground that software can be an essential part of a machine. Some early U.S. software patents were handled clumsily and appeared to cover techniques that were not actually original. See also COMPUTER LAW; COPYRIGHT; SOFTWARE PATENT;

TRADE SECRET.

path

1. a designation that specifies how to find a file on a disk that has more than one directory. In Windows, paths have either of two forms. For example,

\AAA\BBB\CCC

means, “In the root directory there is a directory called AAA. In AAA there is a directory called BBB. In BBB there is a directory or file called CCC.”

If the initial backslash is left out, the path starts at the directory currently in use rather than at the root directory. For example, the path

AAA\BBB\CCC

means, “In the current directory there is a directory called AAA. In AAA there is a directory called BBB. In BBB there is a directory or file called CCC.” Paths in UNIX are written the same way but with forward slashes (/ rather than \).

2.The set of directories in which the computer will look for an executable file when the user types a command. Some software packages have to be on the path in order to work properly. In Windows, the current directory is always treated as if it were on the path; in UNIX it is not, unless explicitly included as “.” (a period).

3.a contour or outline. Objects in a draw program are defined by paths.

See DRAW PROGRAM; POSTSCRIPT; VECTOR GRAPHICS.

4. a line that defines the movement of an object in an animation.

PC any computer whose architecture is derived, however distantly, from the original IBM PC (IBM Personal Computer) of 1981, and which is considered to be part of the same lineage, in contrast to the MACINTOSH,

SUN WORKSTATION, or others.

Today, PC denotes a computer that is built to run Microsoft Windows, although it may equally well run Linux, BSD UNIX, or some other operating system. Despite having adopted a very similar hardware architecture, the Pentium-based Apple Macintosh is not considered to be a PC; instead, it is the PC’s arch-rival.

PC 100, PC 133 the special bus used by the Pentium III to communicate with RAM, at 100 or 133 MHz depending on the model.

PC 2001 a specification issued by Intel and Microsoft for the design of LEGACY-FREE personal computers (i.e., computers that run the latest PC operating systems but are not burdened by the need for full compatibility with the original PC hardware). See LEGACY-FREE.

PC Card a newer name for PCMCIA expansion cards. See PCMCIA; see also EXPRESSCARD and note there.

PC compatibility the ability of a computer to run the same programs and use the same hardware accessories as the original IBM Personal Computer (PC) or newer computers of the same general type. In order to be fully PC-compatible, a computer needs an 8088-family processor (which nowadays means a Pentium or equivalent). Some other computers can software-emulate a Pentium and thereby run PC software on a completely different CPU, such as a Sun RISC CPU or a PowerPC chip.

PCI (Peripheral Component Interface) an improved bus for PC-compatible computers, introduced by Intel in 1992. PCI is faster than EISA and has been expanded to 64 bits to meet the needs of the Pentium processor. PCI-bus computers can use a bus interface unit on the motherboard to connect to EISA or ISA cards, so that the same motherboard has both PCI and ISA slots. See BUS.

PCI Express a faster version of the PCI bus introduced by Intel in 2004 as a replacement for both PCI and AGP, with which it is not compatible. It is not truly a bus, but rather a very high-speed serial communication system. See also EXPRESSCARD.

PCIe, PCI-E see PCI EXPRESS.

PCMCIA (Personal Computer Memory Card International Association) an organization that defines standards for connecting peripherals to miniaturized computers such as notebooks and laptops. The standard ISA, EISA, PCI, and VLB buses are too bulky for laptop computers; the PCMCIA bus (now known as PC Card and CardBus) is a widely accepted standard. See www.pcmcia.org. See also BUS; CARDBUS; EXPRESSCARD.

PDA (personal digital assistant) a pocket-sized, special-purpose personal computer that lacks a conventional keyboard. PDAs do such things as send and receive fax messages, maintain an electronic address book and telephone directory, and serve as notepads on which files can be created for subsequent processing on a larger computer.

PDF (Portable Document Format) a file format representing images of printable pages. PDF files are viewable with Adobe Reader.

See ACROBAT; ADOBE SYSTEMS, INC.

peak a way of measuring the voltage of alternating current from zero volts up to the most positive point. The peak voltage of any symmetrical

waveform is exactly half of the peak-to-peak voltage. See also PEAK-TO- PEAK; RMS.

peak-to-peak a way of measuring the voltage of alternating current from the most positive to the most negative point. For example, the audio output of a microphone is about 0.002 volt peak-to-peak; the “line out” from a piece of audio equipment is about 1 volt peak-to-peak. Peak-to-peak measurement is used mostly with low-level signals that are viewed on oscilloscopes; ordinary voltmeters usually read rms voltage. The peak-to-peak voltage of a sine wave is 2.828 × the rms voltage. Contrast PEAK; RMS.

PEBKAC (humorous) (Problem Exists Between Keyboard And Chair) an uncomplimentary way to indicate that a computer problem is the fault of the user. A legendary, and apparently recurrent, PEBKAC consists of the user mistaking the CD-ROM disk tray for a coffee cup holder and eventually breaking it.

peer-to-peer a network architecture in which there is no central server; all computers are equal participants.

pel (picture element) PIXEL; one of the small dots of which a bitmap image is composed.

pen (in draw or paint programs) a tool used to create lines. Sometimes a similar tool is shown as a pencil. Most programs allow control of the width of the stroke the pen makes, the shape of the nib of the pen, the miter limit, and the shape of the endcaps. See Figure 193.

FIGURE 193. Pen tool

Pentium a high-performance 32-bit microprocessor introduced by Intel in 1993 as the successor to the 486. If the original numbering scheme had been continued, the Pentium would have been the 586, hence its name. The Pentium is software-compatible with the 8088 used in the original IBM PC. Subsequent models (Pentium Pro, Pentium II, Pentium III, and many others) have steadily increased in speed (to about 1000 times that of the original 8088) and have introduced fast caches, 64-bit registers, superscalar pipelining, and multiple cores. Today, the Pentium is the most popular microprocessor for general-purpose computing.

per computer (describing a software license) assigned to a specific computer or set of computers. Most software is licensed per computer; that is, the license gives you the right to install each copy on one computer for the use of anyone who wants to use it there. Contrast PER SEAT, PER USER.

per incident (describing a service plan) charging a fee each time service is requested. Each request is called an incident.

per seat (describing a software license) allowing a specific number of people to use the software at one time.

In some Microsoft documentation, per seat means either PER USER or PER DEVICE, even though neither of these is exactly what others have normally meant by per seat.

See SEAT. Contrast PER COMPUTER, PER USER.

per user (describing a software license) allowing specific people to use the software. For instance, if a software package is licensed for 12 users and installed on a server, then up to 12 user accounts of the server can access the software. Contrast PER COMPUTER, PER SEAT.

peripheral a device connected to a computer. Examples of peripherals include terminals, tape drives, disk drives, and printers.

Perl (Practical Extraction and Report Language) a programming language developed by Larry Wall for writing utilities that perform large amounts of string handling, text file processing, and interaction with the operating system. Like AWK and REXX, which it resembles, Perl is normally interpreted, not compiled. It is designed to minimize the programming effort needed for computations that are relatively simple and quick.

Figure 194 shows a simple Perl program. The overall syntax resembles C. Numbers and strings are interconvertible and are not distinguished; as far as Perl is concerned, 4 = ’4’.

#!/usr/local/bin/perl

@path = split(/:/,$ENV{’PATH’}); $n = 1 + $#path;

FIGURE 194. Perl programming example

Every variable name begins with a character indicating its type: $ for scalars (numbers and strings), @ for ordinary arrays, and % for associative arrays (arrays whose elements are retrieved by keyword rather than by position). Array elements are numbered from 0; the operator $# retrieves the index of the highest element, which is one less than the total number of elements. Lines that begin with # are comments.

Under UNIX, Perl programs are often called scripts and begin with the line

#!/usr/local/bin/perl

so that if the program is passed to UNIX as a SHELL SCRIPT, it will be given to the Perl interpreter for execution.

On the WORLD WIDE WEB, Perl is often used to implement web pages that perform computations. Instead of writing a web page in HTML, the programmer writes a Perl program that generates the HTML from other sources of information, such as database files, calculations, and even the user’s menu choices. See also AWK; CGI; HTML; REXX.

permalink a permanent link; in a BLOG or online newspaper, a permanent link (URL) to a particular article or page, which will remain usable after the article ceases to be today’s news.

permission an attribute of a file that indicates who is allowed to read or modify it. For example, the UNIX command

chmod ugo+r-wx myfile.txt

sets permissions for the user, group, and other users of file myfile.txt by adding read permission (+r) and removing write and execute permission (-wx). In Windows, with NTFS, you can set permissions on a file or directory by right-clicking on it and choosing Properties, Security.

personal computer a computer designed to be used by only one person, either at home or in a business setting. One of the first personal computers was the Digital Equipment Corporation PDP-8, a minicomputer often used in scientific laboratories in the early 1970s. See also

MACINTOSH.

personal digital assistant see PDA.

PERT (Program Evaluation and Review Technique) a method for project planning by analyzing the time required for each step. See PROJECT MANAGEMENT.

peta- metric prefix meaning ×1,000,000,000,000,000 (1015). Peta- is apparently derived from the Greek word for “to fly” or “to soar.” See

METRIC PREFIXES.

PGA

1.pin grid array, the arrangement of pins on a Pentium or similar microprocessor, making it possible to plug the processor into a socket.

2.Professional Graphics Adapter, an early high-performance graphics system for the IBM PC, marketed in the mid-1980s.

PGP (Pretty Good Privacy) a public-key encryption system developed by Philip Zimmerman.

phishing a type of fraud carried out by sending out e-mail that pretends to come from a bank or corporation with which the victim has an account. The e-mail message tells the victim to click on a link in order to handle some kind of urgent business. In reality, both the message and the link are counterfeit, and the victim ends up giving his or her password or credit card information to the phisher, or at the very least, visiting a web site that disseminates MALWARE.

To protect yourself from phishing, do not click on web links that arrive in e-mail. Instead, when you want to contact your bank, type its web address yourself. Some web browsers detect links that are known to be phishing sites, but this is not perfect protection because phishers often change their addresses. See also SMISHING; WHALING.

phone plug a plug of a type originally designed for telephone switchboards, now used on audio equipment. Three sizes are used, each with 2 to 4 conductors. The miniature 3.5-mm 3-conductor phone plug (Figure 195, center) is used for stereo connections to sound cards. Contrast RCA PLUG; RJ-11.

FIGURE 195. Phone plugs

phono plug See RCA PLUG.

phosphorus chemical element (atomic number 15) added to silicon to create an N-type SEMICONDUCTOR.

Photo CD Kodak’s proprietary format for storing digitized photographs on CD-ROM, now seldom used.

photo paper

1.light-sensitive paper used in making conventional photographic prints (not involving a computer).

2.paper that has a glossy coating, but is not light-sensitive, used in inkjet printers for high-quality printing of photographs.

photograph a continuous-tone image created with a camera, either digital or film. Because photographs closely reproduce what we are able to see with our eyes, we credit them with being more “real” than drawings. Photographs make any document more interesting and convey much more information to the readers than words alone.

You can choose to use photographs from collections of stock photographs, take photographs with a digital camera, or have some of your older photographs scanned in.

It’s best to scan the photo at the finished size and at the resolution of the output device (usually your laser printer). The contrast and brightness of the image can be adjusted while scanning it.

You’ll notice that photographs can create large files. A 31⁄2 × 5-inch color snapshot, saved as a 300 DPI, 24-bit (millions of colors), uncompressed TIFF file, creates a 3.3-megabyte file that is too large to e-mail conveniently. It’s best to save to a compressed file format (e.g., JPEG). Files of black-and-white photos are smaller; they don’t have to include as much information.

A photopaint program like Adobe PhotoShop or PhotoShop Elements can be used to improve digital images. Spots and flaws can be removed, distracting elements erased, backgrounds changed, or the overall color balance adjusted. (See RETOUCHING.) Then import the digital photo into your page layout or word processing program, or publish it on the World Wide Web. See DIGITAL CAMERA. Contrast GRAYSCALE.

photopaint program a type of bitmap editing program with special tools and filters for manipulating photographs. You can also create illustrations from scratch with the drawing tools provided. Compare

GRAM. Contrast DRAW PROGRAM.

In many ways, photopaint programs are the professional versions of the limited paint programs that come with operating systems. They are proportionately difficult to learn and master. Be prepared to spend enough time reading the manual and experimenting. See also

AIRBRUSH; BLUR; BRIGHTNESS; CLONE; CONTRAST; EDGE DETECT; FILTER; GIMP; MAGIC WAND; MOTION BLUR; PIXELATE.

FIGURE 196. Photopaint program

PHP a scripting language often used to generate web pages by computation on the server (compare CGI, definition 1; ASP). PHP originated as a set of small, efficient CGI programs to do common tasks, released by Rasmus Lerdorf in 1995. The package was called PHP Tools, short for Personal Home Page Tools. Today, PHP is said to stand for PHP Hypertext Processor (yes, the acronym includes itself; compare GNU).

PHP is available free of charge for a wide range of computers. For more information see www.php.net.

phreak (or phone phreak) a person who makes a game of defrauding telephone companies by means of fake control signals, stolen credit card numbers, and the like. See 2600.

pi the Greek letter π, which stands for a special number that is approximately equal to 3.14159. If the radius of a circle is r, then the circumference is 2πr and the area is πr 2 .

pica (in typesetting) a unit of measurement equal to 12 points. There are approximately 6 picas to one inch (2.54 cm).

FIGURE 197. Pica

pick tool a mouse cursor shaped like an arrow that is used to pick up or pick out (select) objects in an image.

pickup roller in a printer, the roller that picks up pieces of paper from the paper tray. It usually has a soft, rubbery surface. The pickup roller should be cleaned or replaced if the printer is suffering frequent paper jams from the inability to pick up a piece of paper.

pico- metric prefix meaning ÷1,000,000,000,000. Pico- is derived from a Spanish word that means, among other things, “small quantity.” See METRIC PREFIXES.

PICS (Platform for Internet Content Selection) the specifications for META TAGs that label web sites with their content ratings; the standard used by rating systems such as SafeSurf and ICRA.

pictograph

1.a picture that represents an idea. Computer icons are a type of pictograph.

2.a bar graph that uses stacked or stretched symbols instead of plain vertical bars. Although this lends some visual interest to the graph, it can also be confusing if not handled correctly.

pie chart a type of chart that resembles a pie and graphically shows the relative size of different subcategories of a whole. See Figure 248 on page 453.

piece fraction a fraction constructed of three characters: small numerals for the numerator and denominator separated by a forward slash or a hori-

zontal bar (1⁄2, or 12 ). Contrast BUILT FRACTION; CASE FRACTION. See illustration at CASE FRACTION.

pilcrow the symbol ¶, which is used to mark the beginning of a new paragraph when the text is set with continuous paragraphs. The pilcrow can also be used as a footnote symbol. See FOOTNOTE.