P

P

p prefix See pico-.

P prefix See peta-.

P2P or P-to-P n. An Internet-based networking option in which two or more computers connect directly to each other to communicate and share files without use of a central server. Interest in P2P networking blossomed with the introduction of Napster and Gnutella. See also peer-to-peer architecture, peer-to-peer communications. Short for Peer-to-Peer.

P3P n. Acronym for Platform for Privacy Preferences. An open W3C protocol that allows Internet users to control the type of personal information that is collected by the Web sites they visit. P3P uses User Agents built into browsers and Web applications to allow P3P-enabled Web sites to communicate privacy practices to users before they log on to the Web site. P3P compares the Web site s privacy policies with the user s personal set of privacy preferences, and it reports any disagreements to the user.

P5 n. Intel s internal working name for the Pentium microprocessor. Although it was not intended to be used publicly, the name P5 leaked out to the computer-industry trade press and was commonly used to reference the microprocessor before it was released. See also 586, Pentium.

pack vb. To store information in a more compact form. Packing eliminates unnecessary spaces and other such characters and may use other special methods of compressing data as well. It is used by some programs to minimize storage requirements.

package n. 1. A computer application consisting of one or more programs created to perform a particular type of work for example, an accounting package or a spreadsheet package. 2. In electronics, the housing in which an electronic component is packaged. See also DIP. 3. A group of classes or interfaces and a keyword in the Java programming language. Packages are declared in Java by using the package keyword. See also class, declare, interface (definition 1), keyword.

packaged software n. A software program sold through a retail distributor, as opposed to custom software. See also canned software.

packed decimal adj. A method of encoding decimal numbers in binary form that maximizes storage space by using each byte to represent two decimal digits. When signed decimal numbers are stored in packed decimal format, the sign appears in the rightmost four bits of the rightmost (least significant) byte.

packet n. 1. A unit of information transmitted as a whole from one device to another on a network. 2. In packet-switching networks, a transmission unit of fixed maximum size that consists of binary digits representing both data and a header containing an identification number, source and destination addresses, and sometimes error-control data. See also packet switching.

packet assembler and disassembler n. See packet assembler/disassembler.

packet assembler/disassembler n. An interface between non-packet-switching equipment and a packet-switching network. Acronym: PAD.

packet filtering n. The process of controlling network access based on IP addresses. Firewalls will often incorporate filters that allow or deny users the ability to enter or leave a local area network. Packet filtering is also used to accept or reject packets such as e-mail, based on the origin of the packet, to ensure security on a private network. See also firewall, IP address, packet (definition 1).

packet flooding n. A technique employed in a number of DoS (denial of service) attacks in which a flood of packets of data are sent to a target server, overwhelming the computer and rendering it unable to respond to legitimate network requests. Examples of specific types of packet flooding include smurf attacks and SYN flood attacks. See also DoS, packet, smurf attack, SYN flood.

packet header n. The portion of a data packet that precedes the body (data). The header contains data, such as source and destination addresses and control and timing information, that is needed for successful transmission.

Packet Internet Groper n. See ping(definition 1).

packet sniffer n. A hardware and/or software device that examines every packet sent across a network. To work, a packet sniffer must be installed in the same network block as the network it is intended to sniff. Designed as a problem-solving tool to isolate problems degrading network performance, packet sniffers have become security risks on some networks because crackers can use them to capture nonencrypted user IDs, passwords, credit card numbers, e-mail addresses, and other confidential information. See also cracker, packet. Compare monitoring software.

packet switching n. A message-delivery technique in which small units of information (packets) are relayed through stations in a computer network along the best route available between the source and the destination. A packet-switching network handles information in small units, breaking long messages into multiple packets before routing. Although each packet may travel along a different path, and the packets composing a message may arrive at different times or out of sequence, the receiving computer reassembles the original message correctly. Packet-switching networks are considered to be fast and efficient. To manage the tasks of routing traffic and assembling/disassembling packets, such a network requires some intelligence from the computers and software that control delivery. The Internet is an example of a packet-switching network. Standards for packet switching on networks are documented in the International Telecommunication Union (ITU) recommendation X.25. Compare circuit switching.

Packet Switching Exchange n. An intermediary switching station in a packet-switching network.

packet trailer n. The portion of a data packet that follows the body (data). The trailer typically contains information related to error checking and correction. See also packet.

packing density n. The number of storage units per length or area of a storage device. Bits per inch is one measure of packing density.

PackIT n. A file format used on the Apple Macintosh to represent collections of Mac files, possibly Huffman compressed. See also Huffman coding, Macintosh.

PAD n. See packet assembler/disassembler.

pad character n. In data input and storage, an extra character inserted as filler to use up surplus space in a predefined block of a specified length, such as a fixed-length field.

padding n. In data storage, the addition of one or more bits, usually zeros, to a block of data to fill it, to force the actual data bits into a certain position, or to prevent the data from duplicating a bit pattern that has an established meaning, such as an embedded command.

paddle n. An early type of input device often used with computer games especially for side-to-side or up-and-down movements of an on-screen object. A paddle is less sophisticated than a joystick because it permits the user, by turning a dial, to specify movement along only a single axis. The paddle got its name because its most popular use was to control the on-screen paddles in the simple early video games, such as Pong. See the illustration.

Paddle.

paddle switch n. Any switch that has a wide handle. The large on/off switch on many IBM personal computers is one type of paddle switch.

page n. 1. In word processing, the text and display elements to be printed on one side of a sheet of paper, subject to formatting specifications such as depth, margin size, and number of columns. 2. A fixed-size block of memory. When used in the context of a paging memory system, a page is a block of memory whose physical address can be changed via mapping hardware. See also EMS, memory management unit, virtual memory. 3. In computer graphics, a portion of display memory that contains one complete full-screen image; the internal representation of a screenful of information. 4. See Web page.

page banner n. A section of a Web page containing a graphic element and text, such as the page title. Page banners are usually displayed at the top of a Web page. Page banners can also be used to link to other Web sites for advertising purposes. Also called: banner.

page break n. The point at which the flow of text in a document moves to the top of a new page. Most word processors automatically place page breaks when the material on the page reaches a specified maximum. By contrast, a hard or manual page break is a command or a code inserted by the user to force a page break at a specific place in the text. See also form feed.

paged address n. In the 80386, i486, and Pentium paged memory architecture, an address in memory created by combining the processes of segment translation and page translation. In the paged-memory scheme, which requires that the microprocessor s paging feature be enabled, logical addresses are transformed into physical addresses in two steps: segment translation and page translation. The first step, segment translation, converts a logical to a linear address an address that refers indirectly to a physical address. After the linear address is obtained, the microprocessor s paging hardware converts the linear address to a physical address by specifying a page table (an array of 32-bit page specifiers), a page (a 4-KB unit of contiguous addresses within physical memory) within that table, and an offset within that page. This information collectively refers to a physical address.

page-description language n. A programming language, such as PostScript, that is used to describe output to a printer or a display device, which then uses the instructions from the page-description language to construct text and graphics to create the required page image. Page-description languages are like other computer languages, with logical program flow allowing for sophisticated manipulation of the output. A page-description language, like a blueprint, sets out specifications (as for fonts and type sizes) but leaves the work of drawing characters and graphics to the output device itself. Because this approach delegates the detail work to the device that produces the output, a page-description language is machine-independent. These abilities come at a price, however. Page-description languages require printers with processing power and memory comparable to, and often exceeding, that of personal computers. Acronym: PDL. See also PostScript.

paged memory management unit n. A hardware unit that performs tasks related to accessing and managing memory used by different applications or by virtual-memory operating systems. Acronym: PMMU.

Page Down key n. A standard key (often labeled PgDn ) on most computer keyboards whose specific meaning is different in different programs. In many cases, it moves the cursor down to the top of the next page or a specific number of lines.

page fault n. The interrupt that occurs when software attempts to read from or write to a virtual memory location that is marked not present. The mapping hardware of a virtual memory system maintains status information about every page in the virtual address space. A page either is mapped onto a physical address or is not present in physical memory. When a read or write to an unmapped virtual address is detected, the memory management hardware generates the page fault interrupt. The operating system must respond to the page fault by swapping in the data for the page and updating the status information in the memory management unit. See also page (definition 2), swap (definition 2), virtual memory.

page frame n. A physical address to which a page of virtual memory may be mapped. In a system with 4096-byte pages, page frame 0 corresponds to physical addresses 0 through 4095. See also paging, virtual memory.

page-image buffer n. Memory in a page printer used to hold the bit map (image) of a page as the printer s raster image processor builds the page and as the printer produces the page. See also page printer, raster image processor.

page-image file n. A file containing the necessary code for a printer or other display device to create the page or screen image. See also PostScript.

page-jacking n. A deceptive practice that detours Web visitors from legitimate sites generated as search engine results to copycat Web pages, from which they will be redirected to pornographic or other unwanted sites. Page-jacking is accomplished by copying the contents and metatags of a Web page, altering its title and content so that, on search results, it displays before the original, and then submitting the copied page to search engines. When clicking on the link to the copied site, the visitor will instead be redirected to an unwanted and unrelated site. See also metatag. Compare mousetrapping.

page layout n. In desktop publishing, the process of arranging text and graphics on the pages of a document. Page-layout programs excel in text placement and management of special effects applied to text. Although page-layout programs are generally slower than word-processing programs, they can perform such advanced tasks as flowing text into complex multicolumn page designs, printing documents in signatures, managing color separations, and supporting sophisticated kerning and hyphenation.

page makeup n. The assembling of graphics and text on a page in preparation for printing.

page mode RAM n. A specially designed dynamic RAM that supports access to sequential memory locations with a reduced cycle time. This is especially attractive in video RAM, in which each location is accessed in ascending order to create the screen image. Page mode RAM can also improve the execution speed of code because code tends to execute sequentially through memory. See also cycle time, dynamic RAM.

page orientation n. See landscape mode, portrait mode.

page printer n. Any printer, such as a laser printer, that prints an entire page at once. Because page printers must store the entire page in memory before printing, they require relatively large amounts of memory. Compare line printer.

pager n. Pocket-sized wireless electronic device that uses radio signals to record incoming phone numbers or short text messages. Some pagers allow users to send messages as well. Also called: beeper.

page reader n. See document reader.

page setup n. A set of choices that affect how a file is printed on the page. Page setup might reflect the size of paper going into the printer, the page margins, the specific pages in the document to be printed, whether the image is to be reduced or enlarged when printed, and whether another file is to be printed immediately after the first file is printed.

pages per minute n. See PPM.

Page Up key n. A standard key (often labeled PgUp ) on most computer keyboards whose specific meaning is different in different programs. In many cases, it moves the cursor up to the top of the previous page or a specific number of lines.

pagination n. 1. The process of dividing a document into pages for printing. 2. The process of adding page numbers, as in a running head.

paging n. A technique for implementing virtual memory. The virtual address space is divided into a number of fixed-size blocks called pages, each of which can be mapped onto any of the physical addresses available on the system. Special memory management hardware (MMU or PMMU) performs the address translation from virtual addresses to physical addresses. See also memory management unit, paged memory management unit, virtual memory.

paging file n. A hidden file on the hard disk that operating systems (such as Windows, Mac OS X, and UNIX) use to hold parts of programs and data files that do not fit in memory. The paging file and physical memory, or RAM, make up virtual memory. Data is moved from the paging file to memory as needed and moved from memory to the paging file to make room for new data in memory. Also called: swap file. See also virtual memory.

paint¹ n. A color and pattern used with graphics programs to fill areas of a drawing, applied with tools such as a paintbrush or a spraycan.

paint² vb. To fill a portion of a drawing with paint (color or a pattern).

paintbrush n. An artist s tool in a paint program or another graphics application for applying a streak of solid color to an image. The user can usually select the width of the streak. See also paint program. Compare spraycan.

paint program n. An application program that creates graphics as bit maps. A paint program, because it treats a drawing as a group of dots, is particularly appropriate for freehand drawing. Such a program commonly provides tools for images requiring lines, curves, and geometric shapes but does not treat any shape as an entity that can be moved or modified as a discrete object without losing its identity. Compare drawing program.

palette n. 1. In paint programs, a collection of drawing tools, such as patterns, colors, brush shapes, and different line widths, from which the user can choose. 2. A subset of the color look-up table that establishes the colors that can be displayed on the screen at a particular time. The number of colors in a palette is determined by the number of bits used to represent a pixel. See also color bits, color look-up table, pixel.

palmtop n. A portable personal computer whose size enables it to be held in one hand while it is operated with the other hand. A major difference between palmtop computers and laptop computers is that palmtops are usually powered by off-the-shelf batteries such as AA cells. Palmtop computers typically do not have disk drives; rather, their programs are stored in ROM and are loaded into RAM when they are switched on. More recent palmtop computers are equipped with PCMCIA slots to provide wider flexibility and greater capability. See also handheld PC, PCMCIA slot, portable computer. Compare laptop.

PAM n. See pulse amplitude modulation.

panning n. In computer graphics, a display method in which a viewing window on the screen scans horizontally or vertically, like a camera, to bring offscreen extensions of the current image smoothly into view.

PANTONE MATCHING SYSTEM n. In graphic arts and printing, a standard system of ink color specification consisting of a swatch book in which each of about 500 colors is assigned a number. Acronym: PMS. See also color model.

PAP n. 1. Acronym for Password Authentication Protocol. A method for verifying the identity of a user attempting to log on to a Point-to-Point Protocol (PPP) server. PAP is used if a more rigorous method, such as the Challenge Handshake Authentication Protocol (CHAP), is not available or if the user name and password that the user submitted to PAP must be sent to another program without encryption. 2. Acronym for Printer Access Protocol. The protocol in AppleTalk networks that governs communication between computers and printers.

paper feed n. A mechanism that moves paper through a printer. In laser printers and other page printers, the paper feed is usually a series of rollers that firmly grip and align the paper. In dot-matrix printers, the paper feed is usually a pin feed or tractor feed, in which small pins drag or push paper that has detachable edges punched with sprocket holes. Friction feed is another type of paper feed, in which the paper is gripped between the platen and pressure rollers and pulled by rotation of the platen.

paperless office n. The idealized office in which information is entirely stored, manipulated, and transferred electronically rather than on paper.

paper-white adj. Of, pertaining to, or being a type of monochrome computer monitor whose default operating colors are black text on a white background. Paper-white monitors are popular in desktop publishing and word processing environments because the monitor most closely resembles a white sheet of paper printed with black characters.

paper-white monitor n. A display monitor in which text and graphics characters are displayed in black against a white background to resemble the appearance of a printed page. Some manufacturers use the name to refer to a background that is tinted in a manner corresponding to bonded paper.

paradigm n. An archetypal example or pattern that provides a model for a process or system.

paragraph n. 1. In word processing, any part of a document preceded by one paragraph mark and ending with another. To the program, a paragraph represents a unit of information that can be selected as a whole or given formatting distinct from the surrounding paragraphs. 2. On IBM and other computers built around the Intel 8088 or 8086 microprocessor, a 16-byte section of memory beginning at a location (address) that can be divided evenly by 16 (hexadecimal 10).

parallel adj. 1. Of or relating to electronic circuits in which the corresponding terminals of two or more components are connected. 2. In geometry and graphics, of, relating to, or being lines that run side by side in the same direction in the same plane without intersecting. 3. In data communications, of, relating to, or being information that is sent in groups of bits over multiple wires, one wire for each bit in a group. See also parallel interface. Compare serial. 4. In data handling, of or relating to handling more than one event at a time, with each event having its own portion of the system s resources. See also parallel processing.

parallel access n. The ability to store or retrieve all of the bits composing a single unit of information, such as a byte or a word (usually two bytes), at the same time. Also called: simultaneous access.

parallel adder n. A logic device that processes the addition of several (typically 4, 8, or 16) binary inputs simultaneously rather than sequentially, as is the case with half adders and full adders. Parallel adders speed processing because they require fewer steps to produce the result. Compare full adder, half adder.

parallel algorithm n. An algorithm in which more than one portion of the algorithm can be followed at one time. Parallel algorithms are usually used in multiprocessing environments. Compare sequential algorithm.

parallel circuit n. A circuit in which the corresponding leads of two or more of the circuit components are connected. In a parallel circuit, there are two or more separate pathways between points. The individual components in a parallel circuit all receive the same voltage but share the current load. See the illustration. Compare series circuit.

Parallel circuit.

parallel computer n. A computer that uses several processors that work concurrently. Software written for parallel computers can increase the amount of work done in a specific amount of time by dividing a computing task among several simultaneously functioning processors. See also parallel processing.

parallel computing n. The use of multiple computers or processors to solve a problem or perform a function. See also array processor, massively parallel processing, pipeline processing, SMP.

parallel connection n. See parallel interface.

parallel database n. A database system involving the concurrent use of two or more processors or operating system processes to service database management requests such as SQL queries and updates, transaction logging, I/O handling, and data buffering. A parallel database is capable of performing a large number of simultaneous tasks across multiple processors and storage devices, providing quick access to databases containing many gigabytes of data.

Parallel Data Structure n. See PDS (definition 2).

parallel execution n. See concurrent execution.

parallel interface n. The specification of a data transmission scheme that sends multiple data and control bits simultaneously over wires connected in parallel. The most common parallel interface is the Centronics interface. See also Centronics parallel interface. Compare serial interface.

parallel port n. An input/output connector that sends and receives data 8 bits at a time, in parallel, between a computer and a peripheral device such as a printer, scanner, CD-ROM, or other storage device. The parallel port, often called a Centronics interface after the original design standard, uses a 25-pin connector called a DB-25 connector that includes three groups of lines: four for control signals, five for status signals, and eight for data. See also Centronics parallel interface, ECP, EPP, IEEE 1284, input/output port. Compare serial port.

Parallel port.

parallel printer n. A printer that is connected to the computer via a parallel interface. In general, a parallel connection can move data between devices faster than a serial connection can. The parallel interface is preferred in the IBM PC world because its cabling is more standardized than that of the serial interface and because the computer s operating system assumes that the system printer is attached to the parallel port. See also parallel interface. Compare serial printer.

parallel processing n. A method of processing that can run only on a computer that contains two or more processors running simultaneously. Parallel processing differs from multiprocessing in the way a task is distributed over the available processors. In multiprocessing, a process might be divided up into sequential blocks, with one processor managing access to a database, another analyzing the data, and a third handling graphical output to the screen. Programmers working with systems that perform parallel processing must find ways to divide a task so that it is more or less evenly distributed among the processors available. Compare coprocessor, multiprocessing.

parallel server n. A computer system that implements some form of parallel processing to improve its performance as a server. See also SMP server.

parallel transmission n. The simultaneous transmission of a group of bits over separate wires. With microcomputers, parallel transmission refers to the transmission of 1 byte (8 bits). The standard connection for parallel transmission is known as the Centronics interface. See also Centronics parallel interface. Compare serial transmission.

parameter n. In programming, a value that is given to a variable, either at the beginning of an operation or before an expression is evaluated by a program. Until the operation is completed, a parameter is effectively treated as a constant value by the program. A parameter can be text, a number, or an argument name assigned to a value that is passed from one routine to another. Parameters are used as a means of customizing program operation. See also argument, pass by address, pass by value, routine.

parameter-driven adj. Of, pertaining to, or being a program or an operation whose character or outcome is determined by the values of the parameters that are assigned to it.

parameter passing n. In programming, the substitution of an actual parameter value for a formal parameter when a procedure or function call is processed.

parameter RAM n. A few bytes of battery-backed CMOS RAM on the motherboards of Apple Macintosh computers. Information about the configuration of the system is stored in parameter RAM. Acronym: PRAM. See also CMOS RAM. Compare CMOS (definition 2).

PARC n. See Xerox PARC.

parent/child adj. 1. Pertaining to or constituting a relationship between processes in a multitasking environment in which the parent process calls the child process and most often suspends its own operation until the child process aborts or is completed. 2. Pertaining to or constituting a relationship between nodes in a tree data structure in which the parent is one step closer to the root (that is, one level higher) than the child.

parity n. The quality of sameness or equivalence, in the case of computers usually referring to an error-checking procedure in which the number of 1s must always be the same either even or odd for each group of bits transmitted without error. If parity is checked on a per-character basis, the method is called vertical redundancy checking, or VRC; if checked on a block-by-block basis, the method is called longitudinal redundancy checking, or LRC. In typical modem-to-modem communications, parity is one of the parameters that must be agreed upon by sending and receiving parties before transmission can take place. See the table. See also parity bit, parity check, parity error.

Table P.1 Types of Parity.

Type	Description
Even parity	The number of 1s in each successfully transmitted set of bits must be an even number.
Odd parity	The number of 1s in each successfully transmitted set of bits must be an odd number.
No parity	No parity bit is used.
Space parity	A parity bit is used and is always set to 0.
Mark parity	A parity bit is used and is always set to 1.

parity bit n. An extra bit used in checking for errors in groups of data bits transferred within or between computer systems. With PCs, the term is frequently encountered in modem-to-modem communications, in which a parity bit is often used to check the accuracy with which each character is transmitted, and in RAM, where a parity bit is often used to check the accuracy with which each byte is stored.

parity check n. The use of parity to check the accuracy of transmitted data. See also parity, parity bit.

parity error n. An error in parity that indicates an error in transmitted data or in data stored in memory. If a parity error occurs in communications, all or part of a message must be retransmitted; if a parity error occurs in RAM, the computer usually halts. See also parity, parity bit.

park vb. To position the read/write head over a portion of a disk that stores no data (and therefore can never be damaged) or beyond the surface of the disk, prior to shutting down the drive, especially in preparation for moving it. Parking can be performed manually, automatically, or by a disk utility program.

parrallaxing n. A 3-D animation technique, often used by computer game developers, where backgrounds are displayed using different levels of speed to achieve realism. For example, distant levels move at a slower speed than closer levels, thereby giving the illusion of depth. See also animation.

parse vb. To break input into smaller chunks so that a program can act upon the information.

parser n. An application or device that breaks data into smaller chunks so that an application can act on the information. See also parse.

partition n. 1. A logically distinct portion of memory or a storage device that functions as though it were a physically separate unit. 2. In database programming, a subset of a database table or file.

Partition Boot Sector n. The first sector in the system (startup) partition of a computer s bootable hard disk, or the first sector of a bootable floppy disk. On an x86-based computer, the Partition Boot Sector is read into memory at startup by the Master Boot Record. It is the Partition Boot Sector that contains the instructions required to begin the process of loading and starting the computer s operating system. See also Master Boot Record, partition table.

partition table n. A table of information in the first sector of a computer s hard disk that tells where each partition (discrete portion of storage) on the disk begins and ends. The physical locations are given as the beginning and ending head, sector, and cylinder numbers. In addition to these addresses, the partition table identifies the type of file system used for each partition and identifies whether the partition is bootable whether it can be used to start the computer. Although it is a small data structure, the partition table is a critical element on the hard disk.

partnership n. The settings on a desktop computer and Windows CE device that allow information to be synchronized, as well as copied or moved between the computer and device. The mobile device can have partnerships with up to two desktop computers. See also synchronization (definition 6).

Pascal n. A concise procedural language designed between 1967 and 1971 by Niklaus Wirth. Pascal, a compiled, structured language built upon ALGOL, simplifies syntax while adding data types and structures such as subranges, enumerated data types, files, records, and sets. See also ALGOL, compiled language. Compare C.

pASP n. See pocket Active Server Pages.

pass¹ n. In programming, the carrying out of one complete sequence of events.

pass² vb. To forward a piece of data from one part of a program to another. See also pass by address, pass by value.

pass by address n. A means of passing an argument or parameter to a subroutine. The calling routine passes the address (memory location) of the parameter to the called routine, which can then use the address to retrieve or modify the value of the parameter. Also called: pass by reference. See also argument, call. Compare pass by value.

pass by reference n. See pass by address.

pass by value n. A means of passing an argument or a parameter to a subroutine. A copy of the value of the argument is created and passed to the called routine. When this method is used, the called routine can modify the copy of the argument, but it cannot modify the original argument. See also argument, call. Compare pass by address.

passivation n. In Sun Microsystems s J2EE network platform, the process of turning off an enterprise java bean (EJB) by caching it from memory to secondary storage. See also Enterprise JavaBeans, J2EE. Compare activation.

passive hub n. A type of hub used on ARCnet networks that passes signals along but has no additional capability. See also ARCnet. Compare active hub, Intelligent hub.

passive-matrix display n. An inexpensive, low-resolution liquid crystal display (LCD) made from a large array of liquid crystal cells that are controlled by transistors outside of the display screen. One transistor controls an entire row or column of pixels. Passive-matrix displays are commonly used in portable computers, such as laptops and notebooks, because of their thin width. While these displays have good contrast for monochrome screens, the resolution is weaker for color screens. These displays are also difficult to view from any angle other than straight on, unlike active-matrix displays. However, computers with passive-matrix displays are considerably cheaper than those with active-matrix screens. See the illustration. Also called: dual-scan display. See also liquid crystal display, supertwist display, transistor, twisted nematic display. Compare active-matrix display.

Passive-matrix display.

passive node n. A network node that listens for transmissions but is not actively involved in passing them along the network; typical of a node on a bus network. See also bus network, node (definition 2).

Passport n. A suite of personal identification services from Microsoft that consolidates user names, passwords, and other information. With the Passport single sign-in service, a user enters one name and password at any Passport site on the Internet; after signing in to one Passport site, a user can sign in to others without reentering the information. Passport also provides a server-based wallet service that stores credit card and billing information, a Kids Passport service, and a public-profile service. Passport is one of the foundation services of the Microsoft .NET initiative. See also .NET, .NET My Services, single sign-on, wallet.

pass-through adj. 1. In general, a reference to something that acts as an intermediary between other entities. For example, a pass-through proxy server allows external access to an internal (protected) server by passing requests from the requesting client to the server without allowing direct access. 2. Pertaining to a device or connector that moves a signal or set of signals from the input to the output without making any changes. For example, a peripheral device such as a SCSI adapter might have a pass-through parallel I/O port for connecting a printer through the same connector.

password n. The string of characters entered by a user to verify his or her identity to the network. The system compares the code against a stored list of authorized passwords and users. If the code is legitimate, the system allows the user access at whatever security level has been approved for the owner of the password. Ideally a password is a combination of text, numbers, and punctuation or other characters that cannot be guessed at or easily cracked by intruders.

password attack n. An attack on a computer or network in which a password is stolen and decrypted or is revealed by a password dictionary program. The compromised password opens the network to the hacker and may also be used to reveal additional network passwords. See also password sniffing.

Password Authentication Protocol n. See PAP (definition 1).

password protection n. The use of passwords as a means of allowing only authorized users access to a computer system or its files.

password shadowing n. A security system in which an encrypted password is stored in a separate shadow file, and its place is taken by a token representing the password. Password shadowing is used as protection from password attacks. See also password attack, password sniffing.

password sniffing n. A technique employed by hackers to capture passwords by intercepting data packets and searching them for passwords. Also called: packet sniffing.

paste vb. To insert text or a graphic that has been cut or copied from one document into a different location in the same or a different document. See also cut, cut and paste.

patch¹ n. A piece of object code that is inserted in an executable program as a temporary fix for a bug.

patch² vb. In programming, to repair a deficiency in the functionality of an existing routine or program, generally in response to an unforeseen need or set of operating circumstances. Patching is a common means of adding a feature or a function to a program until the next version of the software is released. Compare hack (definition 2), kludge (definition 2).

path n. 1. In communications, a link between two nodes in a network. 2. A route through a structured collection of information, as in a database, a program, or files stored on disk. 3. In programming, the sequence of instructions a computer carries out in executing a routine. 4. In information processing, such as the theory underlying expert (deductive) systems, a logical course through the branches of a tree of inferences leading to a conclusion. 5. In file storage, the route followed by the operating system through the directories in finding, sorting, and retrieving files on a disk. 6. In graphics, an accumulation of line segments or curves to be filled or drawn.

path menu n. In windowed environments, the menu or drop box used to enter the universal naming convention path to a shared network resource.

pathname n. In a hierarchical filing system, a listing of the directories or folders that lead from the current directory to a file. Also called: directory path.

pattern recognition n. 1. A broad technology describing the ability of a computer to identify patterns. The term usually refers to computer recognition of visual images or sound patterns that have been converted to arrays of numbers. 2. The recognition of purely mathematical or textual patterns.

Pause key n. 1. A key on a keyboard that temporarily stops the operation of a program or a command. The Pause key is used, for example, to halt scrolling so that a multiscreen listing or document can be read. 2. Any key that creates a pause in an operation. For example, many game programs have a Pause key, often simply the P key, that temporarily suspends the game.

payload n. The effects caused by a virus or other malicious code. The payload of a virus may include moving, altering, overwriting, and deleting files, or other destructive activity. A virus or worm may contain more than one payload, each with a separate trigger.

PB n. See petabyte.

PB SRAM n. See pipeline burst static RAM.

PBX n. Acronym for Private Branch Exchange. An automatic telephone switching system that enables users within an organization to place calls to each other without going through the public telephone network. Users can also place calls to outside numbers.

PC n. 1. A microcomputer that conforms to the standard developed by IBM for personal computers, which uses a microprocessor in the Intel 80x86 family (or compatible) and can execute the BIOS. See the illustration. See also 8086, BIOS, clone, IBM PC. 2. A computer in IBM s Personal Computer line. Also called: IBM PC. See also PC-compatible (definition 1), personal computer.

PC.

PCB n. See printed circuit board.

PC board n. See printed circuit board.

PC Card n. An add-in card that conforms to the PCMCIA specification. A PC Card is a removable device, approximately the same size as a credit card, that is designed to plug into a PCMCIA slot. Release 1 of the PCMCIA specification, introduced in June 1990, specified a Type I card that is 3.3 millimeters thick and is intended to be used primarily as a memory-related peripheral. Release 2 of the PCMCIA specification, introduced in September 1991, specifies both a 5-millimeter-thick Type II card and a 10.5-millimeter-thick Type III card. Type II cards accommodate devices such as modem, fax, and network cards. Type III cards accommodate devices that require more space, such as wireless communications devices and rotating storage media (such as hard disks). See also PCMCIA, PCMCIA slot.

PC Card slot n. See PCMCIA slot.

PC-compatible adj. Conforming to IBM PC/XT and PC/AT hardware and software specifications, which have been the de facto standard in the computing industry for personal computers that use the Intel 80x86 family or compatible chips. Most PC-compatible computers today are developed outside of IBM; they are still sometimes referred to as clones. Also called: IBM PC. See also 8086, clone, de facto standard, IBM AT, Wintel.

PC-DOS n. Acronym for Personal Computer Disk Operating System. The version of MS-DOS sold by IBM. MS-DOS and PC-DOS are virtually identical, although file names of utility programs sometimes differ in the two versions. See also MS-DOS.

PC Expo n. Annual exposition centering on issues relating to the personal computer industry. PC Expo encompasses product exhibitions and educational events covering a wide range of topics affecting personal computing.

P-channel MOS n. See PMOS.

PCI n. See PCI local bus.

PCI card n. Short for Peripheral Component Interconnect card. A card that fits into a PCI local bus to add functionality to a PC. Examples of the types of PCI cards available include TV tuner cards, video adapters, and network interface cards. See also card, PCI local bus.

PCI expansion slot n. A connection socket for a peripheral designed for the Peripheral Component Interconnect (PCI) local bus on a computer motherboard.

PCI Industrial Computer Manufacturers Group n. See PICMG.

PCI local bus n. Short for Peripheral Component Interconnect local bus. A specification introduced by Intel Corporation that defines a local bus system that allows up to 10 PCI-compliant expansion cards to be installed in the computer. A PCI local bus system requires the presence of a PCI controller card, which must be installed in one of the PCI-compliant slots. Optionally, an expansion bus controller for the system s ISA, EISA, or Micro Channel Architecture slots can be installed as well, providing increased synchronization over all the system s bus-installed resources. The PCI controller can exchange data with the system s CPU either 32 bits or 64 bits at a time, depending on the implementation, and it allows intelligent, PCI-compliant adapters to perform tasks concurrently with the CPU using a technique called bus mastering. The PCI specification allows for multiplexing, a technique that permits more than one electrical signal to be present on the bus at one time. See also local bus. Compare VL bus.

PCIX n. 1. Acronym for Peripheral Component Interconnect Extended. A computer bus technology developed by IBM, Compaq, and Hewlett-Packard that allows data to be transferred at greater speeds. PCIX increases the speed of data from 66 MHz to 133 MHz, but it will not run faster than the connected peripherals or computer processor will allow. PCI and PCIX peripherals are compatible with one another. Also called: PCI-X. 2. Acronym for Permission-based Customer Information Exchange. A framework for the organization and exchange of information between customer and vendor. PCIX allows different companies to map information into a customer-friendly, permission-based format without changing internal database structures.

PCL n. See Printer Control Language.

PCM n. See pulse code modulation.

PCMCIA n. Acronym for Personal Computer Memory Card International Association. A group of manufacturers and vendors formed to promote a common standard for PC Card based peripherals and the slot designed to hold them, primarily on laptop, palmtop, and other portable computers, as well as for intelligent electronic devices. PCMCIA is also the name of the standard for PC Cards, first introduced in 1990 as release 1. See also PC Card, PCMCIA slot.

PCMCIA card n. See PC Card.

PCMCIA connector n. The 68-pin female connector inside a PCMCIA slot designed to hold the 68-pin male connector on a PC Card. See also PC Card, PCMCIA slot.

PCMCIA slot n. An opening in the housing of a computer, peripheral, or other intelligent electronic device designed to hold a PC Card. Also called: PC Card slot. See also PC Card, PCMCIA connector.

PC memory card n. 1. An add-in circuit card that increases the amount of RAM in a system. See also memory card. 2. A Type I PC Card as specified by PCMCIA. In this context, such a card consists of conventional static RAM chips powered by a small battery and is designed to provide additional RAM to the system. See also PC Card. Compare flash memory.

PCMIA device n. See PC Card.

p-code n. See pseudocode.

PCS n. See Personal Communications Services.

PCT n. 1. Acronym for program comprehension tool. A software engineering tool that facilitates the process of understanding the structure and/or functionality of computer programs. 2. Acronym for Private Communications Technology, a protocol standard drafted by Microsoft and submitted to the IETF for consideration. PCT, like the Netscape-designed SSL (Secure Sockets Layer), supports authentication and encryption for securing privacy in Internet communications. 3. Acronym for Personal Communications Technology. An enhanced version of Secure Sockets Layer (SSL).

.pcx n. The file extension that identifies bitmapped images in the PC Paintbrush file format.

PC/XT n. The second-generation of the original IBM Personal Computer. The IBM PC/XT was introduced in 1983 and was the first of the PC computers to support hard disks. See also IBM PC.

PC/XT keyboard n. The keyboard for the PC/XT. Strong, reliable, and equipped with 83 keys, the PC/XT keyboard offers a typist an audible click. See also IBM PC, PC/XT.

PDA n. Acronym for Personal Digital Assistant. A lightweight palmtop computer designed to provide specific functions like personal organization (calendar, note taking, database, calculator, and so on) as well as communications. More advanced models also offer multimedia features. Many PDA devices rely on a pen or other pointing device for input instead of a keyboard or mouse, although some offer a keyboard too small for touch typing to use in conjunction with a pen or pointing device. For data storage, a PDA relies on flash memory instead of power-hungry disk drives. See also firmware, flash memory, handheld PC, PC Card, pen computer.

PDC n. See Primary Domain Controller.

PD-CD drive n. Short for phase change rewritable disc-compact disc drive. A storage device that combines a CD-ROM drive and a phase change rewritable disc (PD) drive, which can store up to 650 megabytes of data on cartridges of rewritable optical discs. See also phase-change recording.

PDD n. Acronym for Portable Digital Document. A graphics file created from a document by QuickDraw GX under Mac OS. PDDs are stored in a form that is independent of printer resolution; they print at the highest resolution available on the printer used; and they can contain the original fonts used in the document. Therefore, a PDD can be printed by a computer other than the one on which it was created.

.pdf n. The file extension that identifies documents encoded in the Portable Document Format developed by Adobe Systems. To display or print a .pdf file, the user should obtain the freeware Adobe Acrobat Reader. See also Acrobat, Portable Document Format.

PDL n. See page-description language.

PDM n. See pulse duration modulation.

PDO n. See Portable Distributed Objects.

PDS n. 1. Acronym for Processor Direct Slot. An expansion slot in Macintosh computers that is connected directly to the CPU signals. There are several kinds of PDS slots with different numbers of pins and different sets of signals, depending on which CPU is used in a particular computer. 2. Acronym for Parallel Data Structure. A hidden file, located in the root directory of a disk that is shared under AppleShare, that contains access privilege information for folders.

Peachy virus n. A virus, first detected in 2001, that was the first to attempt to spread itself through PDF files. The Peachy virus takes advantage of an Adobe Acrobat feature that enables users to embed files in PDF documents. The embedded Peachy virus file infects the computer of a user who downloads the PDF file and then opens the file in Adobe Acrobat.

peek vb. 1. To read a byte from an absolute memory location. Peek commands are often found in programming languages such as Basic that do not normally allow access to specific memory locations. 2. To look at the next character in a buffer associated with an input device without actually removing the character from the buffer.

peer n. Any of the devices on a layered communications network that operate on the same protocol level. See also network architecture.

peer-to-peer architecture n. A network of two or more computers that use the same program or type of program to communicate and share data. Each computer, or peer, is considered equal in terms of responsibilities and each acts as a server to the others in the network. Unlike a client/server architecture, a dedicated file server is not required. However, network performance is generally not as good as under client/server, especially under heavy loads. Also called: peer-to-peer network. See also peer, peer-to-peer communications, server. Compare client/server architecture.

peer-to-peer communications n. Interaction between devices that operate on the same communications level on a network based on a layered architecture. See also network architecture.

peer-to-peer network n. See peer-to-peer architecture.

PE file n. See portable executable file.

pel n. See pixel. Short for picture element.

PEM n. See Privacy Enhanced Mail.

pen n. See light pen, stylus.

pen-based computing n. The process of entering handwritten symbols into a computer via a stylus and pressure-sensitive pad. See also pen computer.

pen computer n. Any of a class of computers whose primary input device is a pen (stylus) instead of a keyboard. A pen computer is usually a smaller, handheld device and has a flat semiconductor-based display such as an LCD display. It requires either a special operating system designed to work with the pen input device or a proprietary operating system designed to work with a specific-purpose device. The pen computer is the primary model for an emerging class of computers known as personal digital assistants (PDAs). See also clipboard computer, PC Card, PDA.

Penguin n. Slang for the Linux operating system or a Linux user. The name comes from the penguin character used as the Linux mascot. See also Tux.

pen plotter n. A traditional graphics plotter that uses pens to draw on paper. Pen plotters use one or more colored pens, either fiber-tipped pens or, for highest-quality output, drafting pens. See also plotter. Compare electrostatic plotter.

Pentium n. A family of 32-bit microprocessors introduced by Intel in March 1993 as the successor to the i486. The Pentium family is composed of superscalar, CISC-based microprocessors containing between 3 million (earlier models) and 28 million transistors. They have a 32-bit address bus, a 64-bit data bus, a built-in floating-point unit and memory management unit, built-in caches, and a System Management Mode (SMM), which provides the microprocessor with the ability to slow or halt some system components when the system is idle or performing non-CPU-intensive tasks, thereby lessening power consumption. The Pentium also employs branch prediction, resulting in faster system performance. In addition, the Pentium has built-in features to ensure data integrity, and it supports functional redundancy checking (FRC). The Pentium II introduced MMX media enhancement support. See also branch prediction, CISC, functional redundancy checking, i486DX, L1 cache, L2 cache, microprocessor, MMX, P5, SIMD, superscalar.

Pentium upgradable n. 1. An i486 motherboard capable of being adapted to run a Pentium-class processor. See also i486DX, microprocessor, motherboard, Pentium. 2. A 486 PC that can be upgraded to Pentium class by adding a Pentium processor. See also i486DX.

perfboard n. See breadboard. Short for perforated fiber board.

performance monitor n. A process or program that appraises and records status information about various system devices and other processes.

period n. The length of time required for an oscillation to complete one full cycle. For an oscillating electrical signal, the period is the time between waveform repetitions. If f is the frequency of oscillation in hertz, and t is the period in seconds, then t = 1/f. See the illustration.

Period. The period of an oscillating signal.

peripheral n. In computing, a device, such as a disk drive, printer, modem, or joystick, that is connected to a computer and is controlled by the computer s microprocessor. Also called: peripheral device. See also console.

Peripheral Component Interconnect n. See PCI local bus.

peripheral device n. See peripheral.

peripheral power supply n. An auxiliary source of electricity used by a computer or a device as a backup in case of a power failure. Acronym: PPS.

Perl n. Acronym for Practical Extraction and Report Language. An interpreted language, based on C and several UNIX utilities. Perl has powerful string-handling features for extracting information from text files. Perl can assemble a string and send it to the shell as a command; hence, it is often used for system administration tasks. A program in Perl is known as a script. Perl was devised by Larry Wall at NASA s Jet Propulsion Laboratory.

permanent storage n. A recording medium that retains the data recorded on it for long periods of time without power. Ink on paper is by far the most widely used permanent storage, but data can be transferred from paper to a computer only with difficulty. Typically, some form of magnetic medium, such as floppy disk or tape, is preferable. Magnetic media are generally accepted as permanent, even though the magnetic fields that encode data in the media tend to fade eventually (in five years or more). See also nonvolatile memory.

permanent swap file n. In Windows, a file composed of contiguous disk sectors used for virtual memory operations. See also swap file, virtual memory.

permanent virtual circuit n. See PVC.

permission n. In a networked or multiuser computer environment, the ability of a particular user to access a particular resource by means of his or her user account. Permissions are granted by the system administrator or other authorized person. Several levels of access can be given: read only, read and write (view and change), or read, write, and delete. Also called: Access permission.

permission class n. A class that defines access to a resource or defines an identity by supporting authorization checks.

permission object n. An instance of a permission class that represents access rights to resources or identity. A permission object can be used to specify a request, a demand, or a grant of permission.

permissions log n. A file on a network or multiuser computer environment where permissions for users are stored. When a user attempts to access a resource on the system, the permissions log is checked to see whether the user has permission to use it.

perpendicular recording n. A method of increasing storage capacity on magnetic media by aligning the magnetic dipoles, whose orientation determines bit values, in a direction that is perpendicular to the recording surface. Also called: vertical recording.

per-pixel lighting n. A lighting scheme used in 3D computer game rendering and other digital animation applications that calculates proper lighting for every pixel displayed. Per-pixel lighting allows highly realistic lighting effects but requires significant video card capabilities to display properly. Also called: Phong shading.

Per Seat Licensing n. A licensing mode that requires a separate Client Access License for each client computer, regardless of whether all the clients access the server at the same time. See also client. Compare Per Server Licensing.

Per Server Licensing n. A licensing mode that requires a separate Client Access License for each concurrent connection to the server, regardless of whether there are other client computers on the network that do not happen to connect concurrently. Compare Per Seat Licensing.

persistence n. A characteristic of some light-emitting materials, such as the phosphors used in CRTs, that causes an image to be retained for a short while after being irradiated, as by an electron beam in a CRT. The decay in persistence is sometimes called luminance decay.

persistent client connection n. See persistent connection.

persistent connection n. A connection to a client that remains open after a server sends a response. Included in HTTP 1.1 and similar to the Netscape HTTP 1.0 Keep Alive extension, persistent connections are used to improve Internet efficiency and performance by eliminating the overhead associated with multiple connections. Also called: persistent client connection. See also pipelining (definition 1).

persistent data n. Data that is stored in a database or on tape so that it is retained by the computer between sessions.

persistent link n. See hot link (definition 1).

persistent storage n. Memory that remains intact when the power to a device is turned off, such as ROM. See also memory.

Personal Communications Services n. Term used by the United States Federal Communications Commission (FCC) to cover a range of wireless, all-digital communications technologies and services, including cordless phones, voice mail, paging, faxing, and personal digital assistants (PDAs). Personal Communications Services, or PCS, is divided into narrowband and broadband categories. Narrowband, which operates in the 900 MHz band of frequencies, provides paging, data messaging, faxing, and one- and two-way electronic messaging capabilities. Broadband, which operates in the 1850 MHz to 1990 MHz range and is considered the next-generation PCS, enables two-way voice, data, and video communications. The cellular phone technologies known as GSM (Global System for Mobile Communications), CDMA (Code Division Multiple Access), and TDMA (Time Division Multiple Access) are included in the PCS category. Acronym: PCS. Compare Code Division Multiple Access, Global Systems for Mobile Communications, Time Division Multiple Access.

personal computer n. A computer designed for use by one person at a time. Personal computers do not need to share the processing, disk, and printer resources of another computer. IBM PC compatible computers and Apple Macintoshes are both examples of personal computers. Acronym: PC.

Personal Computer n. See IBM PC.

Personal Computer Memory Card International Association n. See PCMCIA.

personal digital assistant n. See PDA.

personal finance manager n. A software application designed to assist the user in performing simple financial accounting tasks, such as balancing checkbooks and paying bills.

Personal Handyphone System n. A device developed in Japan to act as a cellular phone that can handle phone, FAX, and voice. Acronym: PHS.

personal identification number n. See PIN.

personal information manager n. See PIM.

personalization technology n. An e-commerce marketing technique in which Web sites and services analyze the interests of individual customers. The e-business then uses this information to deliver services, product offerings, and advertising that match each customer s personal interests.

Personal Web Server n. Microsoft applications that allow a computer running the Windows family of operating systems to function as a Web server for publishing personal Web pages and intranet sites. Personal Web Server is available as part of Microsoft Windows NT 4.0 Option Pack (NTOP), Windows 98, and Windows 95 OEM Service Release 2. FrontPage Personal Web Server is available as part of FrontPage 1.1, FrontPage 97, FrontPage 98, and FrontPage 2000.

perspective view n. In computer graphics, a display method that shows objects in three dimensions (height, width, and depth), with the depth aspect rendered according to the desired perspective. An advantage of perspective view is that it presents a more accurate representation of what the human eye perceives. Compare isometric view.

peta- prefix Denotes 1 quadrillion (10¹⁵). In computing, which is based on the binary (base 2) numbering system, peta- has a literal value of 1,125,899,906,842,624, which is the power of 2 (2⁵⁰) closest to 1 quadrillion. Abbreviation: P.

petabyte n. Either 1 quadrillion bytes or 1,125,899,906,842,624 bytes.Abbreviation: PB.

PGA n. See pin grid array, Professional Graphics Adapter.

PgDn key n. See Page Down key.

PGP n. Acronym for Pretty Good Privacy. A program for public key encryption, using the RSA algorithm, developed by Philip Zimmermann. PGP software is available in unsupported free versions and supported commercial versions. See also privacy, public key encryption, RSA encryption.

PgUp key n. See Page Up key.

phage virus n. A destructive virus that affects the Palm operating system (OS). Phage copies itself, overwriting application files and destroying them. Once the first host file is infected, Phage will spread to all available files. Phage may be spread from one Palm device to another by beaming or connection with a docking station. Phage was one of the first viruses created specifically to affect handheld wireless devices and the first to impact the Palm OS.

phase n. A relative measurement that describes the temporal relationship between two signals that have the same frequency. Phase is measured in degrees, with one full oscillation cycle having 360 degrees. The phase of one signal can lead or follow the other by 0 through 180 degrees. See the illustration.

Phase. The ratio of a to b is the phase difference, expressed in degrees.

phase-change recording n. In optical media, a recording technique that uses a laser beam focused on a microscopic portion of metallic crystal to alter the reflectiveness of its structure in such a way that the change can be read as a 0 bit or 1 bit, depending on whether the resulting structure reflects or absorbs the laser light. See also PD-CD drive.

phase encoding n. 1. The process of placing digital information on an analog carrier wave while periodically changing the phase of the carrier to increase the bit density of the transmission. See also Manchester coding, phase. 2. A recording technique used with magnetic storage devices in which each data-holding unit is divided into two parts, each of which is magnetized so that it is opposite in polarity to the other.

phase-locked adj. Of, pertaining to, or characteristic of the relationship between two signals whose phases relative to each other are kept constant by a controlling mechanism, such as an electronic device.

phase modulation n. A method of imposing information onto a waveform signal by shifting the phase of the wave to represent information, such as the binary digits 0 and 1. See the illustration. See also phase-shift keying.

Phase modulation. A phase shift of 180 degrees.

phase-shift keying n. A communications method used by modems to encode data that relies on phase shifts in a carrier wave to represent digital information. In its simplest form, phase-shift keying allows the phase of the carrier wave to be in either of two states: shifted 0 degrees or shifted 180 degrees, effectively reversing the phase of the wave. This straightforward phase-shift keying, however, is useful only when each phase can be measured against an unchanging reference value, so a more sophisticated technique called differential phase-shift keying, or DPSK, is used in many modems. In differential phase-shift keying, the phase of the carrier wave is shifted to represent more than two possible states, and each state is interpreted as a relative change from the state preceding it. No reference values or timing considerations are required and because more than two states are possible, more than one binary digit can represent each state. Acronym: PSK. See also phase modulation.

Phoenix BIOS n. An IBM-compatible ROM BIOS manufactured by Phoenix Technologies, Ltd. A popular ROM BIOS in many so-called PC clone computers, the Phoenix BIOS was an early leader among the IBM-compatible computers shortly after they began to appear in the marketplace. See also BIOS, ROM BIOS. Compare AMI BIOS.

phone connector n. An attachment, usually an RJ-11 connector, used to join a telephone line to a device such as a modem. See the illustration.

Phone connector.

phoneline networking n. The use of telephone wiring for connecting computers and other devices in a small network, such as a home network. See also HomePNA.

phoneme n. In linguistics, the smallest unit of speech that distinguishes one word sound from another. Phonemes are the elements on which computer speech is based.

phono connector n. An attachment used to connect a device, such as a microphone or a pair of headphones, to a piece of audio equipment or to a computer peripheral or adapter with audio capability. See the illustration.

Phono connector.

phosphor n. Any substance capable of emitting light when struck by radiation. The inside surface of a CRT screen is coated with a phosphor that, when excited by an electron beam, displays an image on the screen. See also persistence.

PhotoCD n. A digitizing system from Kodak that allows 35mm film pictures, negatives, slides, and scanned images to be stored on a compact disc. Images are stored in a file format called Kodak PhotoCD IMAGE PAC File Format, or PCD. Many photography or film development businesses offer this service. Images stored on a PhotoCD can usually be viewed by any computer with CD-ROM capabilities and the software required to read PCD. Such images can also be viewed using one of a variety of players designed to display images stored on CDs.

photo cell n. See photoelectric device.

photocomposition n. In traditional typesetting, the use of photographic and electronic equipment in laying out and producing a printed page. In desktop publishing, phototypesetters are used to accomplish the same ends. See also phototypesetter. Compare imagesetter.

photoconductor n. A material that exhibits increased conductivity when it is exposed to a source of light. Photoconductors are used in photodetectors, which are used in fiber optics to register light and convert it into electrical pulses. See also fiber optics.

photo editor n. A graphics application used to manipulate an image, such as a scanned photograph, digitally.

photoelectric device n. A device that uses light to create or modulate an electric signal. A photoelectric device uses semiconductor material and falls in one of two categories. In one type (photocell), light falling on the semiconductor generates an electrical current. In another type of device (photosensor), light changes the resistance of the semiconductor material, modulating an applied voltage.

photolithography n. A technique used in the fabrication of integrated circuits. The circuit pattern is drawn, photographed, and reduced to a negative having the desired final size. This negative is called the photomask. Light is passed through the photomask onto a wafer made of semiconductor material that has been coated with a photoresistive material. Where light strikes the photoresistive material, its composition is changed. In the next step, the photoresistive material not affected by light is washed off. Finally, the semiconductor material is exposed to an etching solution that eats away the surface not protected by the photoresistive material, creating the desired circuit pattern on the surface of the wafer. See also photomask, photoresist.

photomask n. A photographic negative image of a circuit pattern used in fabrication of integrated circuits. See also photolithography.

photonics n. Optoelectronic systems that transmit visible light or infrared energy. Photonic systems are used with fiber optic networks and optical circuits. Photonic networks offer dramatic increases in speed and bandwidth, allowing significantly greater amounts of information to be encoded and transmitted than with traditional cabling solutions.

photorealism n. The process of creating images that are as close to photographic or real-life quality as possible. In computer graphics, photorealism requires powerful computers and highly sophisticated software and is heavily mathematical. See also ray tracing.

photoresist n. A compound that is used in photolithographic fabrication of integrated circuits and printed circuit boards. When exposed to ultraviolet light through a photomask, the photoresistive material exposed to the light polymerizes (hardens); the areas not exposed can be washed away, leaving the pattern of traces on the substrate. Subsequent etching removes areas not protected by the polymerized photoresist.

photosensor n. See photoelectric device.

Photoshop n. Adobe software product for digital image editing and enhancement, photo retouching, and color management of graphic images. Photoshop includes such features as multiple undo, text editing with formatting control, and enhanced color management and controls. The program supports numerous Web and graphics file formats and runs on both the Windows and Power Macintosh platforms.

phototypesetter n. A printer similar to a laser printer but capable of resolutions over 2,000 dots per inch. Phototypesetters apply light directly to a photographic film or photosensitive paper. See also photocomposition. Compare imagesetter.

photovoltaic cell n. See solar cell.

PHP n. Acronym for PHP: Hypertext Preprocessor. An open source scripting language used with HTML documents to execute server-side interactive functions. PHP runs on all major operating systems and is primarily used with Linux and UNIX Web servers or on Windows servers with add-on software. PHP may be embedded in a Web page and used to access and present database information. An HTML document that contains a PHP script usually has a .php filename extension. Originally PHP stood for Personal Home Page, with later versions standing for PHP Hypertext Preprocessor or simply PHP. The syntax of PHP is fairly simple and very similar to that of Perl, with some aspects of Bourne shell, JavaScript, and C. It can also be regarded as a technology (server-side environment for ported script engines, like ASP).

phreak¹ n. A person who breaks into, or cracks, telephone networks or other secured systems. In the 1970s, the telephone system used audible tones as switching signals, and phone phreaks used homebrew hardware to match the tones and steal long-distance service. See also homebrew. Compare cracker, hacker (definition 2).

phreak² vb. To break into, or crack, phone networks or computer systems. See also homebrew. Compare hack.

PHS n. See Personal Handyphone System.

physical adj. In computing, of, pertaining to, or characteristic of a real, as opposed to a conceptual, piece of equipment or frame of reference. Compare logical (definition 2).

physical address n. An address that corresponds to a hardware memory location. In simple processors such as the 8088 and the 68000, every address is a physical address. In processors supporting virtual memory, programs reference virtual addresses, which are then mapped by memory management hardware onto physical addresses. Also called: hardware address. See also memory management unit, paging, virtual memory.

physical-image file n. A hard disk copy of the material to be recorded onto a CD-ROM. Creating a complete copy precludes problems in writing the CD-ROM because of delays in assembling the material from a scattered group of files. See also CD-ROM. Compare virtual-image file.

physical layer n. The first, or lowest, of the seven layers in the ISO/OSI reference model for standardizing computer-to-computer communications. The physical layer is totally hardware-oriented and deals with all aspects of establishing and maintaining a physical link between communicating computers. Among specifications covered on the physical layer are cabling, electrical signals, and mechanical connections. See the illustration. See also ISO/OSI reference model.

Physical layer. Lowest layer in the ISO/OSI reference model.

physical memory n. Memory actually present in the system, as opposed to virtual memory. A computer might have 64 megabytes of physical RAM but support a virtual memory capacity of 1 gigabyte or more. Compare virtual memory.

physical network n. One of two ways of describing the topology, or layout, of a computer network; the other is logical network. A physical network refers to the actual configuration of the hardware forming a network that is, to the computers, connecting hardware, and especially the cabling patterns that give the network its shape. Basic physical layouts include the bus, ring, and star topologies. See also bus network, logical network, ring network, star network.

physical storage n. See real storage.

pi n. A mathematical constant equal to approximately 3.1415926535897932, describing the ratio of the circumference of a circle to its diameter.

PIC n. See programmable interrupt controller.

pica n. 1. With reference to typewriters, a fixed-width type font that fits 10 characters to the linear inch. See also pitch. 2. As used by typographers, a unit of measure equal to 12 points or approximately 1/6 inch. See also point¹ (definition 1).

PICMG n. Acronym for the PCI Industrial Computer Manufacturers Group. A consortium of more than 350 computer product vendors, this non-profit organization develops specifications for PCI-based devices, such as the CompactPCI specification. See also CompactPCI.

pico- prefix Denotes one trillionth (10 ¹²), or, in the British numbering system, one million millionth. Abbreviation: p.

picoJava n. A microprocessor developed by Sun Microsystems, Inc., that executes Java code. See also Java.

picosecond n. One trillionth of a second. Abbreviation: psec.

PICS n. See Platform for Internet Content Selection.

.pict n. The file extension that identifies graphic images in the Macintosh PICT format. See also PICT.

PICT n. A file-format standard for encoding graphical images, both object-oriented and bitmapped. The PICT file format was first used in Macintosh applications, but many PC applications can read the format too. See also bitmapped graphics, object-oriented graphics.

picture element n. See pixel.

pie chart n. A type of graph that presents values as percentages (slices) of a whole (a pie).

piezoelectric adj. Of, pertaining to, or characteristic of crystals that can convert between mechanical and electrical energy. An electric potential applied to a piezoelectric crystal causes a small change in the shape of the crystal. Likewise, physical pressure applied to the crystal creates an electrical potential difference between the surfaces of the crystal.

piggyback board n. A printed circuit board that plugs into another circuit board to enhance its capabilities. A piggyback board is sometimes used to replace a single chip, in which case the chip is removed and the piggyback board is inserted into the empty socket. See also daughterboard.

Pilot n. A series of popular handheld personal digital assistants (PDAs) designed by Palm and based on the Palm OS operating system. Palm introduced its first Pilot model in 1996, followed in 1997 by the PalmPilot, and thereafter by a series of other Palm handheld models.

PILOT n. Acronym for Programmed Inquiry, Learning or Teaching. A programming language developed in 1976 by John A. Starkweather and designed primarily for creating applications for computer-aided instruction.

PIM n. Acronym for personal information manager. An application that usually includes an address book and organizes unrelated information, such as notes, appointments, and names, in a useful way.

pin n. A slender prong. Pins are commonly encountered as the contacts protruding from a male connector. Connectors are often identified by the number of pins they have. Other types of pins are the spidery, leglike metal appendages that connect computer chips to sockets on a circuit board or directly to the circuit board. See the illustration.

Pin. A 16-pin DIP (top) and a 6-pin DIN (bottom).

PIN n. Acronym for personal identification number. A unique code number used to gain access to personal information or assets via an electronic device. PINs are used by a variety of electronic services such as automated bank tellers, Internet sites, and wireless phone services.

pinch roller n. A small cylindrical pulley that presses magnetic tape against the drive s capstan to move the tape over the tape machine s heads. See also capstan.

pinch-roller plotter n. A type of plotter, intermediate between drum and flatbed types, that uses hard rubber or metal wheels to hold the paper against the main roller. See also plotter. Compare drum plotter, flatbed plotter.

pin-compatible adj. Having pins that are equivalent to the pins on another chip or device. A chip, for example, might have different internal circuitry from that used in another chip, but if the two chips use the same pins for input and output of identical signals, they are pin-compatible. Compare plug-compatible.

pine n. Acronym for pine is not elm, or for Program for Internet News and E-mail. One of the most commonly encountered programs for reading and composing e-mail on character-based UNIX systems. The pine program was developed as an improved version of elm at the University of Washington. Compare elm.

pin feed n. A method of feeding paper through a printer in which small pins, mounted on rollers on the ends of the platen, engage holes near the edges of continuous-form paper. See also continuous-form paper, paper feed. Compare tractor feed.

ping¹ n. 1. Acronym for Packet Internet Groper. A protocol for testing whether a particular computer is connected to the Internet by sending a packet to its IP address and waiting for a response. The name actually comes from submarine active sonar, where a sound signal called a ping is broadcast, and surrounding objects are revealed by their reflections of the sound. 2. A UNIX utility that implements the ping protocol.

ping² vb. 1. To test whether a computer is connected to the Internet using the ping utility. 2. To test which users on a mailing list are current by sending e-mail to the list asking for a response.

Ping of Death n. A form of Internet vandalism that entails sending a packet that is substantially larger than the usual 64 bytes over the Internet via the ping protocol to a remote computer. The size of the packet causes the computer to crash or reboot. See also packet (definition 2), ping¹ (definition 1).

ping packet n. An are you there message transmitted by a Packet Internet Groper program. A ping packet is sent from one node to the IP (Internet Protocol) address of a network computer to determine whether that node is able to send and receive transmissions. Many shareware and freeware ping utilities for PCs are available for download from the Internet. See also ping¹ (definition 1), packet¹ (definition 1).

ping pong n. 1. In communications, a technique that changes the direction of transmission so that the sender becomes the receiver and vice versa. 2. In information processing and transfer, the technique of using two temporary storage areas (buffers) rather than one to hold both input and output.

ping-pong buffer n. A double buffer in which each part is alternately filled and flushed, resulting in a more or less continuous stream of input and output data. See also ping pong (definition 2).

pin grid array n. A method of mounting chips on boards, preferred for chips with a very large number of pins. Pin grid array packages have pins protruding from the bottom surface of the chip, as opposed to dual in-line packages and leaderless chip carrier packages, which have pins protruding from the edges. Acronym: PGA. Compare DIP, leadless chip carrier.

pink contract n. A non-standard addendum to a contract with an Internet service provider (ISP), specifically offering the client the opportunity to send unsolicited commercial e-mail and put up spam-related Web sites. See also spam.

pinout n. A description or diagram of the pins of a chip or connector. See also pin.

PIO n. Acronym for Programmed Input/Output (or, less frequently, Processor Input/Output). One of two transfer methods used in moving data between a disk drive and memory. With PIO, the disk controller moves a block of data into the CPU s registers, and the CPU then moves the data to its intended destination. PIO is characteristic of IDE drives. The alternative data-transfer method, direct memory access (DMA), bypasses the CPU and moves data directly between disk and memory. See also Bus, bus mastering, controller. Compare direct memory access.

pipe n. 1. A portion of memory that can be used by one process to pass information along to another. Essentially, a pipe works like its namesake: it connects two processes so that the output of one can be used as the input to the other. See also input stream, output stream. 2. The vertical line character ( ) that appears on a PC keyboard as the shift character on the backslash (\) key. 3. In MS-DOS and UNIX, a command function that transfers the output of one command to the input of a second command.

pipeline burst static RAM n. A type of static RAM that uses burst and pipelining technologies to increase the speed at which information can be provided to a computer s CPU. By pipelining requests so that one is being acted upon at the same time the next is getting underway, pipeline burst static RAM, or PB SRAM, can provide information to the CPU at high speed. PB SRAM is used in L2 caches (rapid-response memory dedicated to storing frequently requested data) on computers running at bus speeds of 75 MHz or higher. Acronym: PB SRAM. See also burst (definition 2), L2 cache, pipelining, static RAM. Compare asynchronous static RAM, dynamic RAM, synchronous burst static RAM.

pipeline processing n. A method of processing on a computer that allows fast parallel processing of data. This is accomplished by overlapping operations using a pipe, or a portion of memory that passes information from one process to another. See also parallel processing, pipe (definition 1), pipelining (definition 3).

pipelining n. 1. A method of fetching and decoding instructions (preprocessing) in which, at any given time, several program instructions are in various stages of being fetched or decoded. Ideally, pipelining speeds execution time by ensuring that the microprocessor does not have to wait for instructions; when it completes execution of one instruction, the next is ready and waiting. See also superpipelining. 2. In parallel processing, a method in which instructions are passed from one processing unit to another, as on an assembly line, and each unit is specialized for performing a particular type of operation. 3. The use of pipes in passing the output of one task as input to another until a desired sequence of tasks has been carried out. See also pipe (definition 1), pour.

piracy n. 1. The theft of a computer design or program. 2. Unauthorized distribution and use of a computer program.

.pit n. A file extension for an archive file compressed with PackIT. See also PackIT.

pitch n. A measure, generally used with monospace fonts, that describes the number of characters that fit in a horizontal inch. See also characters per inch, screen pitch. Compare point¹ (definition 1).

PivotChart adj. A graphical tool in Microsoft Excel or Access that can be used to display data from a list or database in chart form. Based on user-selected information incorporated in an Excel PivotTable report or list, a PivotChart report provides the ability to chart the data interactively for example, to pivot the chart s point of view from product sales by category to product sales by region or by salesperson. See also PivotTable.

PivotTable adj. An interactive table in Microsoft Excel or Access that can show the same data from a list or a database in more than one arrangement. A user can manipulate the rows and columns in a PivotTable to view or summarize the information in different ways for purposes of analysis. In Excel, a PivotTable report is the basis for creating a PivotChart report that displays the same data in chart form. See also PivotChart.

pivot year n. In Year 2000 windowing, a date in a 100-year period that serves as the point from which correct dates can be calculated in systems or software that can store only 2-digit years. For example, a pivot year of 1970 means that the numbers 70 through 99 are interpreted as the years 1970 to 1999, and the numbers 00 through 69 as the years 2000 through 2069. See also windowing.

pixel n. Short for picture (pix) element. One spot in a rectilinear grid of thousands of such spots that are individually painted to form an image produced on the screen by a computer or on paper by a printer. A pixel is the smallest element that display or print hardware and software can manipulate in creating letters, numbers, or graphics. See the illustration. Also called: pel.

Pixel. The letter A is actually made up of a pattern of pixels in a grid, as is the cat s eye.

pixel image n. The representation of a color graphic in a computer s memory. A pixel image is similar to a bit image, which also describes a screen graphic, but a pixel image has an added dimension, sometimes called depth, that describes the number of bits in memory assigned to each on-screen pixel.

pixel map n. A data structure that describes the pixel image of a graphic, including such features as color, image, resolution, dimensions, storage format, and number of bits used to describe each pixel. See also pixel, pixel image.

PJL n. See Printer Job Language.

PJ/NF n. Acronym for projection-join normal form. See normal form (definition 1).

PKUNZIP n. A shareware utility program that uncompresses files compressed by the PKZIP shareware utility program. PKUNZIP is generally made available with PKZIP; distribution of PKUNZIP for commercial purposes is not permitted without obtaining permission from its publisher, PKware, Inc. See also PKZIP.

PKZIP n. A widely used shareware utility program for compressing files. Developed by PKware, Inc., in 1989 and available from a wide variety of sources, PKZIP can combine one or more files into a compressed output file having the extension .zip. A companion utility program, PKUNZIP, is required to uncompress the compressed files. See also PKUNZIP, shareware, utility program.

PLA n. Acronym for programmable logic array. See field-programmable logic array.

placeholder n. 1. A character that masks or hides another character for security reasons. For example, when a user types a password, an asterisk is displayed on the screen to take the place of each character typed. 2. Text or some other element used in an application as an indicator that the user should enter in his or her own text.

Plain Old Telephone Service n. See POTS.

plaintext n. 1. Nonencrypted or decrypted text. See also decryption, encryption. 2. A file that is stored as plain ASCII data. Compare ciphertext.

plain vanilla adj. Ordinary; the standard version of hardware or software without any enhancements. For example, a plain vanilla modem might have data transfer capability but no fax or voice features.

.plan n. A file in a UNIX user s home directory that is displayed when other users finger that account. Users can enter information into .plan files at their discretion to provide information in addition to that normally displayed by the finger command. See also finger.

planar adj. 1. In computer graphics, lying within a plane. 2. In the fabrication of semiconductor materials, maintaining the original flat surface of the silicon wafer throughout processing, while the chemicals that make up the elements that control the flow of current are diffused into (and beneath) the surface.

planar transistor n. A special form of transistor that is fabricated with all three elements (collector, emitter, and base) on a single layer of semiconductor material. The structure of a planar transistor permits it to dissipate relatively large amounts of heat, making this design suitable for power transistors. See the illustration.

Planar transistor.

plasma display n. See gas-discharge display.

plastic leadless chip carrier n. See PLCC.

plastic transistor n. A transistor produced entirely from plastic rather than the traditional silicon. A plastic transistor is flexible enough to be embedded in curved surfaces or folded. Production of plastic transistors begins with a thin piece of clear plastic, onto which layers of plastic are printed or sprayed through a mesh. The result is a lightweight, flexible and transparent transistor that can be manufactured in high volumes for a fraction of the cost of silicon transistors. The flexibility and low-cost of plastic transistors make them useful in applications from transparent foldable displays to one-use product containers. See also electronic paper.

platen n. The cylinder in most impact printers and typewriters, around which the paper wraps and against which the print mechanism strikes the paper. The paper bail, a spring-loaded bar with small rollers, holds the paper smoothly against the platen just above the print mechanism.

platform n. 1. The foundation technology of a computer system. Because computers are layered devices composed of a chip-level hardware layer, a firmware and operating-system layer, and an applications program layer, the bottommost layer of a machine is often called a platform. 2. In everyday usage, the type of computer or operating system being used.

Platform for Internet Content Selection n. A specification for rating and labeling Internet content. Originally developed by the World Wide Web Consortium to enable parents, teachers, administrators, and other caretakers to control the material to which children have online access, its use has expanded to include the protection of privacy and intellectual property. PICS is not itself a system for rating Internet content. Rather, it specifies the format conventions to be used by rating systems in devising labels that can be read by PICS-compatible software. Acronym: PICS.

Platform for Privacy Preference Project n. See P3P.

Platform for Privacy Preferences n. See P3P.

platform invoke n. The functionality provided by the run time to enable managed code to call unmanaged native DLL entry points.

platter n. One of the individual metal data storage disks within a hard disk drive. Most hard disks have from two to eight platters. See the illustration. See also hard disk.

Platter.

player n. In relation to digital audio, a program that plays music and other audio files that have been ripped (transferred from a compact disc to a hard disk) and then encoded in a playable format, such as MP3. See also encoder, MP3, ripper.

PlayStation n. Sony Corporation s console computer entertainment gaming system. PlayStation 2, the latest version, is a 128-bit system that features a 300-Mhz processor, 32 MB of Direct RDRAM main memory, and a floating-point performance of 6.2 GFLOPS. PlayStation 2 also offers the capability to play CDs and DVDs. See also computer game, console game. Compare Dreamcast, GameCube, Xbox.

PL/C n. A version of the PL/I programming language developed at Cornell University and used on mainframe computers. See also PL/I.

PLCC n. Acronym for plastic leadless chip carrier. An inexpensive variation of the leadless chip carrier (LCC) method of mounting chips on boards. Although the two carriers are similar in appearance, PLCCs are physically incompatible with leadless chip carriers, which are made from a ceramic material. See also leadless chip carrier.

PLD n. See programmable logic device.

PL/I n. Acronym for Programming Language I (One). A programming language developed by IBM (1964 1969), designed to bring together the key features of FORTRAN, COBOL, and ALGOL while introducing such new concepts as condition-based error handling and multitasking. The result of this effort was a compiled, structured language that was so complex that it never gained widespread acceptance. Nevertheless, PL/I is still used in some academic and research environments. See also ALGOL, COBOL, compiled language, FORTRAN.

PL/M n. Acronym for Programming Language for Microcomputers. A programming language derived from PL/I and developed in the early 1970s by Intel Corporation for microprocessors. PL/M was used primarily for the creation of operating systems. See also PL/I.

plot vb. To create a graphic or a diagram by connecting points representing variables (values) that are defined by their positions in relation to a horizontal (x) axis and a vertical (y) axis (and sometimes a depth, or z, axis).

plotter n. Any device used to draw charts, diagrams, and other line-based graphics. Plotters use either pens or electrostatic charges and toner. Pen plotters draw on paper or transparencies with one or more colored pens. Electrostatic plotters draw a pattern of electrostatically charged dots on the paper and then apply toner and fuse it in place. Plotters use three basic types of paper handling: flatbed, drum, and pinch roller. Flatbed plotters hold the paper still and move the pen along both x and y axes. Drum plotters roll the paper over a cylinder. The pen moves along one axis while the drum, with the paper attached, moves along the other. Pinch-roller plotters are a hybrid of the two, in which the pen moves only along one axis while the paper is moved back and forth by small rollers.

PL/SQL n. Short for Procedural Language Extension to SQL. Oracle s data manipulation language that allows sequenced or grouped execution of SQL statements and is commonly used to manipulate data in an Oracle database. The syntax is similar to the Ada programming language.

plug n. A connector, especially a male connector, one that fits into a socket. See also male connector.

plug and play n. 1. Generally, a reference to the ability of a computer system to automatically configure a device added to it. Plug and play capability exists in Macintoshes based on the NuBus and, since Windows 95, on PC-compatible computers. 2. When capitalized and, especially, when abbreviated PnP, a set of specifications developed by Intel and Microsoft that allows a PC to configure itself automatically to work with peripherals such as monitors, modems, and printers. A user can plug in a peripheral and play it without manually configuring the system. A Plug and Play PC requires both a BIOS that supports Plug and Play and a Plug and Play expansion card. Abbreviation: PnP. See also BIOS, expansion board, peripheral.

plugboard n. A board that permits users to control the operation of a device by plugging cables into sockets.

plug-compatible adj. Equipped with connectors that are equivalent both in structure and in usage. For example, most modems having DB-25 connectors on their rear panels are plug-compatible that is, one can be replaced by another without the cable having to be rewired. Compare pin-compatible.

plug-in n. 1. A small software program that plugs into a larger application to provide added functionality. 2. A software component that plugs into the Netscape Navigator. Plug-ins permit the Web browser to access and execute files embedded in HTML documents that are in formats the browser normally would not recognize, such as many animation, video, and audio files. Most plug-ins are developed by software companies who have proprietary software in which the embedded files are created. Compare helper application.

p-machine n. See pseudomachine.

PMML n. Acronym for Predictive Model Markup Language. An XML-based language that enables sharing of defined predictive models between compliant vendor applications.

PMMU n. See paged memory management unit.

PMOS n. Acronym for P-channel metal-oxide semiconductor. A MOSFET semiconductor technology in which the conduction channel is formed by the movement of holes (electron vacancies created as electrons move from atom to atom) rather than electrons. Because holes move more slowly than electrons do, PMOS is slower than NMOS, but it is also easier and less expensive to fabricate. See also MOS, MOSFET, P-type semiconductor. Compare CMOS, NMOS.

PMS n. See PANTONE MATCHING SYSTEM.

PNG n. Acronym for Portable Network Graphics. A file format for bitmapped graphic images, designed to be a replacement for the GIF format, without the legal restrictions associated with GIF. See also GIF.

PNNI n. Short for Private Network-to-Network Interface. A routing protocol used in ATM networks that provides switches with the ability to communicate changes in the network. Through PNNI, switches can be informed of changes to the network as they occur and can then use the information to make appropriate routing decisions. See also ATM.

PnP n. See plug and play (definition 2).

PNP n. See PNP transistor.

PNP transistor n. A type of bipolar transistor in which a base of N-type material is sandwiched between an emitter and a collector of P-type material. The base, emitter, and collector are the three terminals of the transistor through which current flows. In a PNP transistor, holes (electron vacancies ) are the majority of the charge carriers, and they flow from the emitter to the collector. See the illustration. See also N-type semiconductor, P-type semiconductor. Compare NPN transistor.

PNP transistor.

pocket Active Server Pages n. A scaled-down version of the Active Server Pages optimized for server-side Mobile Channels scripting. Acronym: pASP.

pocket Excel n. A scaled-down version of Microsoft Excel for the Pocket PC. See also Microsoft Excel.

Pocket PC n. A personal handheld computing device based on specifications designed by Microsoft and running the Microsoft Windows for Pocket PC operating system. Pocket PCs maintain the look of a Windows operating system display screen and offer compact versions of many of the applications that run on Windows-powered personal computers. A number of manufacturers produce Pocket PCs, including Hewlett-Packard, Compaq, and Casio.

pocket Word n. A scaled-down version of Microsoft Word for the Pocket PC. See also Microsoft Word.

point¹ n. 1. A unit of measure used in printing, equal to approximately ¹/₇₂ of an inch. Character height and the amount of space (leading) between lines of text are usually specified in points. 2. A single pixel on the screen, identified by its row and column numbers. 3. A location in a geometric form, represented by two or more numbers that constitute its coordinates.

point² vb. To move an arrow or other such indicator to a particular item or position on the screen by using direction keys or by maneuvering a pointing device such as a mouse.

point-and-click adj. Enabling a user to select data and activate programs by using a mouse or other pointing device to move a cursor to a desired location ( point ) and pressing a button on the mouse or other pointing device ( click ).

PointCast n. An Internet service that delivers and displays a personalized set of news articles to individual users. Unlike the World Wide Web and other Internet applications, PointCast is a push technology, where the server automatically uploads data without a specific command from the client. See also server (definition 2).

point chart n. See scatter diagram.

point diagram n. See scatter diagram.

pointer n. In programming and information processing, a variable that contains the memory location (address) of some data rather than the data itself. See also address¹ (definition 1), handle (definition 1), mouse pointer, reference¹.

pointing device n. An input device used to control an on-screen cursor for such actions as pressing on-screen buttons in dialog boxes, choosing menu items, and selecting ranges of cells in spreadsheets or groups of words in a document. A pointing device is often used to create drawings or graphical shapes. The most common pointing device is the mouse, which was popularized by its use with the Apple Macintosh. Other pointing devices include graphics tablets, styluses, light pens, joysticks, pucks, and trackballs. See also graphics tablet, joystick, light pen, mouse, puck, stylus, trackball.

point listing n. A database of popular Web sites categorized by topics of interest and often rated by design and content.

point of presence n. 1. A point in a wide area network to which a user can connect with a local telephone call. 2. A point at which a long distance telephone carrier connects to a local telephone exchange or to an individual user. Acronym: POP.

point of sale n. See POS.

point-to-point configuration n. A communications link in which dedicated links exist between individual origins and destinations, as opposed to a point-to-multipoint configuration, in which the same signal goes to many destinations (such as a cable TV system), or a switched configuration, in which the signal moves from the origin to a switch that routes the signal to one of several possible destinations. Also called: point-to-point connection.

point-to-point connection n. See point-to-point configuration.

point-to-point message system n. In Sun Microsystems s J2EE network platform, a messaging system that uses message queues to store asynchronous, formatted data for coordinating enterprise applications. Each message is addressed to a specific queue, and client applications retrieve messages from the queues. See also asynchronous, J2EE.

Point-to-Point Protocol n. See PPP.

point-to-point tunneling n. A means of setting up secure communications over an open, public network such as the Internet. See also PPTP.

Point-to-Point Tunneling Protocol n. See PPTP.

Poisson distribution n. A mathematical curve often used in statistics and simulation to represent the likelihood of some event occurring, such as the arrival of a customer in a queue, when the average likelihood is known. This distribution, named after the French mathematician S. D. Poisson, is simpler to calculate than the normal and binomial distributions. See also binomial distribution, normal distribution.

poke vb. To store a byte into an absolute memory location. PEEK (read a byte from memory) and POKE commands are often found in programming languages, such as Basic, that do not normally allow access to specific memory locations.

polar coordinates n. Coordinates of the form (r, q) used to locate a point in two dimensions (on a plane). The polar coordinate r is the length of the line that starts at the origin and ends at the point, and q (Greek theta) is the angle between that line and the positive x-axis. Compare Cartesian coordinates.

polarity n. The sign of the potential (voltage) difference between two points in a circuit. When a potential difference exists between two points, one point has a positive polarity and the other a negative polarity. Electrons flow from negative to positive; by convention, however, current is considered to flow from positive to negative.

polarized component n. A circuit component that must be installed with its leads in a particular orientation with respect to the polarity of the circuit. Diodes, rectifiers, and some capacitors are examples of polarized components.

polarizing filter n. A transparent piece of glass or plastic that polarizes the light passing through it; that is, it allows only waves vibrating in a certain direction to pass through. Polarizing filters are often used to reduce glare on monitor screens. See also glare filter.

Polish notation n. See prefix notation.

polling n. See autopolling.

polling cycle n. The time and sequence required for a program to poll each of its devices or network nodes. See also autopolling.

polygon n. Any two-dimensional closed shape composed of three or more line segments, such as a hexagon, an octagon, or a triangle. Computer users encounter polygons in graphics programs.

polyline n. An open shape consisting of multiple connected segments. Polylines are used in CAD and other graphics programs. See also CAD.

polymorphism n. In an object-oriented programming language, the ability to redefine a routine in a derived class (a class that inherited its data structures and routines from another class). Polymorphism allows the programmer to define a base class that includes routines that perform standard operations on groups of related objects, without regard to the exact type of each object. The programmer then redefines the routines in the derived class for each type, taking into account the characteristics of the object. See also class, derived class, object (definition 2), object-oriented programming.

Pong n. The first commercial video game, a table tennis simulation, created by Nolan Bushnell of Atari in 1972.

pop vb. To fetch the top (most recently added) element of a stack, removing that element from the stack in the process. Compare push¹ (definition 1).

POP n. See point of presence, Post Office Protocol.

POP3 n. Acronym for Post Office Protocol 3. This is the current version of the Post Office Protocol standard in common use on TCP/IP networks. See also Post Office Protocol, TCP/IP.

populate vb. 1. To put chips in the sockets of a circuit board. 2. To import prepared data into a database from a file using a software procedure rather than by having a human operator enter individual records.

pop-under ad n. An advertisement on the Internet that appears in a new window in the background, behind the Web site content. Users may be unaware of the presence of pop-under ads until they close foreground windows at the end of a Web session. Pop-under ads may appear in response to a mouse click, a rollover, or after a user has spent a predetermined amount of time at a Web site. See also pop-up ad.

pop-up ad n. An advertisement on the Internet that appears in a new window in the foreground, often whenever a new page is opened within a site. Pop-up ads may appear in response to a mouse click, a rollover, or after a user has spent a predetermined amount of time at a Web site. See also pop-under ad.

pop-up Help n. An online help system whose messages appear as pop-up windows when the user clicks on a topic or area of the screen about which help is desired. Typically, a special form of click, such as clicking the right mouse button or Option-clicking, will activate pop-up Help, if it is available. See also Balloon Help.

pop-up menu or popup menu n. In a graphical user interface, a menu that appears on-screen when a user selects a certain item. Pop-up menus can appear anywhere on the screen and generally disappear when the user selects an item in the menu. Also called: popup. Compare drop-down menu, pull-down menu.

pop-up messages n. The messages that appear when pop-up Help is used.

pop-up window n. A window that appears when an option is selected. Typically, the window remains visible until the mouse button is released.

port¹ n. 1. An interface through which data is transferred between a computer and other devices (such as a printer, mouse, keyboard, or monitor), a network, or a direct connection to another computer. The port appears to the CPU as one or more memory addresses that it can use to send or receive data. Specialized hardware, such as in an add-on circuit board, places data from the device in the memory addresses and sends data from the memory addresses to the device. Ports may also be dedicated solely to input or to output. Ports typically accept a particular type of plug used for a specific purpose. For example, a serial data port, a keyboard, and a high-speed network port all use different connectors, so it s not possible to plug a cable into the wrong port. Also called: input/output port. 2. port number.

port² vb. 1. To change a program in order to be able to run it on a different computer. 2. To move documents, graphics, and other files from one computer to another.

port 25 blocking n. An anti-spam technique adopted by many ISPs to prevent bulk mailings of unsolicited commercial e-mail. Spammers may try to use SMTP servers to relay a single commercial e-mail to multiple recipients. Port 25 blocking filters prevent this spam distribution method. Although it is a popular remedy for some spam problems, port 25 blocking may cause problems for legitimate users of non-compatible e-mail programs.

portable adj. 1. Capable of running on more than one computer system or under more than one operating system. Highly portable software can be moved to other systems with little effort, moderately portable software can be moved only with substantial effort, and nonportable software can be moved only with effort similar to or greater than the effort of writing the original program. 2. Light enough, rugged enough, and free enough of encumbering external connections to be carried by a user.

portable computer n. Any computer designed to be moved easily. Portable computers can be characterized by size and weight. See the table.

Table P.2 Portable Computers.

Type	Approximate weight	Power source	Comments
Transportable	15 30 lb.	House current	Sometimes called luggable; usually has floppy and harddrives; standard CRT screen.
Laptop	8 15 lb.	House current or batteries	Can be held on the lap; usually has a floppy drive;uses flat LCD or plasma screen.
Ultralight	2 8 lb.	Batteries or transformer pack	Easy to carry in a briefcase; sometimes uses RAM drive or EPROM instead of floppy or hard drive; thinner models are known as notebook computers.
Handheld	Less than 2 lb.	Batteries or transformer pack	Also called palmtop or palm-sized; can be held in one hand.

Portable Digital Document n. See PDD.

Portable Distributed Objects n. Software from NeXT, running under UNIX, that supports an object model in which objects to be stored at various locations on a network can be accessed as though they were at a single location. Acronym: PDO.

Portable Document Format n. The Adobe specification for electronic documents that use the Adobe Acrobat family of servers and readers. Acronym: PDF. See also Acrobat, .pdf.

portable executable file n. The file format used for executable programs as well as for files that are linked together to form executable programs.

portable keyboard n. A portable keyboard for use with personal digital assistants (PDAs), wireless phones with advanced digital features, and other handheld mobile devices. Light, compact, and easy to carry, most portable keyboards fold for convenient storage and connect to the handheld device via a built-in cradle.

portable language n. A language that runs in the same way on different systems and therefore can be used for developing software for all of them. C, FORTRAN, and Ada are portable languages because their implementations on different systems are highly uniform; assembly language is extremely nonportable.

Portable Network Graphics n. See PNG.

portal n. A Web site that serves as a gateway to the Internet. A portal is a collection of links, content, and services designed to guide users to information they are likely to find interesting news, weather, entertainment, commerce sites, chat rooms, and so on. Yahoo!, Excite, MSN.com, and Netscape NetCenter are examples of portals. See also home page (definition 1), Web site.

port enumerator n. In Windows, part of the Plug and Play system that detects I/O ports and reports them to the configuration manager. See also plug and play (definition 2).

port expander n. A hardware mechanism used for connecting several devices to a single port. Although several devices might be connected, only one can use the port at any given moment.

portmapper n. A service used by Remote Procedure Call (RPC) to assign port numbers. RPC doesn t follow the Well-Known Ports port designations, and only Portmapper is assigned a permanent port number. Because hackers may gain access to portmapper communication, various portmapper security tools are often used to prevent theft of information. See also remote procedure call.

port number n. A number that enables IP packets to be sent to a particular process on a computer connected to the Internet. Some port numbers, called well-known port numbers, are permanently assigned; for example, e-mail data under SMTP goes to port number 25. A process such as a telnet session receives an ephemeral port number when it starts; data for that session goes to that port number, and the port number goes out of use when the session ends. A total of 65,535 port numbers are available for use with TCP, and the same number are available for UDP. See also IP, Simple Mail Transfer Protocol, socket (definition 1), TCP, UDP. Compare IP address.

portrait mode n. A vertical print orientation in which a document is printed across the narrower dimension of a rectangular sheet of paper. This is the print mode typical of most letters, reports, and other such documents. Compare landscape mode.

portrait monitor n. A monitor with a screen shape higher than it is wide. The proportions (but not necessarily the size) of the screen are usually the same as for a sheet of 8¹/₂-by-11-inch paper. Compare landscape monitor.

port replicator n. A device that enables easy connection of portable computers to less portable devices, such as printers, monitors, and full-sized keyboards. Instead of having to connect each such device individually to a portable computer, a user can plug it permanently into a port replicator and use it simply by plugging the computer into a single socket, also on the port replicator. Port replicators are comparable to docking stations, but without the same capability for expansion and storage. Also called: convenience adapter. See also docking station, port.

POS n. Acronym for point of sale. The place in a store at which goods are paid for. Computerized transaction systems, such as those in use at automated supermarkets, use scanners for reading tags and bar codes, electronic cash registers, and other special devices to record purchases at this point.

POSIT n. Acronym for Profiles for Open Systems Internetworking Technology. A set of nonmandatory standards for U.S. government network equipment. POSIT, which recognizes the prevalence of TCP/IP, is the successor to GOSIP. See also GOSIP, TCP/IP.

positional notation n. In mathematics, a form of notation whose meaning relies in part on the relative location of the elements involved. For example, common numeric notation is positional notation. In the decimal number 34, the position of the numeral 3 signifies three 10s and the position of the numeral 4 signifies four 1s.

POSIX n. Acronym for Portable Operating System Interface for UNIX. An Institute of Electrical and Electronics Engineers (IEEE) standard that defines a set of operating-system services. Programs that adhere to the POSIX standard can be easily ported from one system to another. POSIX was based on UNIX system services, but it was created in a way that allows it to be implemented by other operating systems. See also service (definition 2).

post¹ n. See article.

post² vb. 1. To submit an article in a newsgroup or other online conference or forum. The term is derived from the posting of a notice on a physical bulletin board. See also newsgroup. 2. To place a file on a server on a network or on a Web site.

POST n. See power-on self test.

posterization n. See contouring.

postfix notation n. A form of algebraic notation in which the operators appear after the operands. Also called: reverse Polish notation. Compare infix notation, prefix notation.

postmaster n. The logon name (and therefore the e-mail address) of an account that is responsible for maintaining e-mail services on a mail server. When an account holder is having trouble with e-mail, a message to postmaster or [e-mail] will usually reach a human who can solve the problem.

post office n. The server and associated storage and mail handling services that provide the centralized location for collection and distribution of e-mail over a network.

Post Office Protocol n. A protocol for servers on the Internet that receive, store, and transmit e-mail and for clients on computers that connect to the servers to download and upload e-mail. Acronym: POP.

postprocessor n. A device or a software routine, such as a linker, that operates on data manipulated first by another processor. See also back-end processor (definition 2). Compare preprocessor.

PostScript n. A page-description language from Adobe Systems that offers flexible font capability and high-quality graphics. The most well-known page-description language, PostScript uses English-like commands to control page layout and to load and scale outline fonts. Adobe Systems is also responsible for Display PostScript, a graphics language for computer displays that gives users of both PostScript and Display PostScript absolute WYSIWYG (what-you-see-is-what-you-get), which is difficult when different methods are used for displaying and printing. See also outline font, page-description language.

PostScript font n. A font defined in terms of the PostScript page-description language rules and intended to be printed on a PostScript-compatible printer. PostScript fonts are distinguished from bitmapped fonts by their smoothness, detail, and faithfulness to standards of quality established in the typographic industry. See also PostScript. Compare screen font.

pot n. See potentiometer.

potential n. See electromotive force.

potentiometer n. A circuit element that can be adjusted to provide varying amounts of resistance. The twist-knob and slider-type volume controls on many radios and television sets are potentiometers. Also called: pot.

POTS n. Acronym for Plain Old Telephone Service. Basic dialup telephone connections to the public switched network without any added features or functions. A POTS line is nothing but a phone line connected to a simple, single-line telephone instrument.

pour vb. To send a file or the output from a program to another file or to a device using a pipe. See also pipe (definition 1).

power n. 1. In mathematics, the number of times a value is multiplied by itself for example, 10 to the third power means 10 times 10 times 10. 2. In computing, the electricity used to run a computer. 3. The speed at which a computer performs and the availability of various features. See also computer power.

PowerBook n. Any of several computers in the family of portable Macintosh computers made by Apple.

power conditioning n. A feature of uninterruptible power supply (UPS) that removes spikes, surges, sags, and noise from the power supply. Also called: line conditioning. See also UPS.

power down vb. To shut down (a computer); to turn off the power.

power failure n. Loss of electricity, which causes a loss of unsaved data in a computer s random access memory (RAM) if no backup power supply is connected to the machine. Compare surge.

Power Mac n. See Power Macintosh.

Power Macintosh n. A Macintosh computer based on the PowerPC processor. The first Power Macintoshes, 6100/60, 7100/66, and 8100/80, were unveiled in 1994. Several upgraded versions followed, and in early 1999 the G3, a PowerPC 750, was released. This was followed later in the year with the unveiling of the Power Macintosh G4. The Power Mac G4 uses the PowerPC 7400 processor and features significant boosts in processing speed. The Power Mac G4 uses Apple s Velocity Engine to process information in 128-bit chunks, allowing sustained performance in excess of one gigaflop. Also called: Power Mac. See also PowerPC.

power management n. The regulation of power consumption on a computer, especially a portable battery-operated device such as a laptop. Power management reduces power to certain components, such as the screen and CPU, to use power efficiently and extend battery life. See also ACPI, Advanced Power Management.

Power-on key n. A special key on the Apple ADB and Extended keyboards used for turning on a Macintosh II. The Power-on key is marked with a left-pointing triangle and is used in lieu of the on/off switch. There is no Power-off key; the system is shut down by choosing the Shut Down command from the Special menu.

power-on self test n. A set of routines stored in a computer s read-only memory (ROM) that tests various system components such as RAM, the disk drives, and the keyboard to see whether they are properly connected and operating. If problems are found, these routines alert the user by sounding a series of beeps or displaying a message, often accompanied by a diagnostic numeric value, to the standard output or standard error device (usually the screen). If the power-on self test is successful, it passes control to the system s bootstrap loader. Acronym: POST. See also bootstrap loader.

PowerPC n. A microprocessor architecture developed in 1992 by Motorola and IBM, with some participation by Apple. A PowerPC microprocessor is RISC-based and superscalar, with a 64-bit data bus and 32-bit address bus. It also has separate data and instruction caches, although the size of each varies by implementation. All PowerPC microprocessors have multiple integer and floating-point units. The voltage and operating speed varies with the implementation. Starting with the PowerPC 740, the microprocessors were manufactured with copper, instead of aluminum, for better performance and reliability. See also L1 cache, L2 cache, microprocessor, RISC, superscalar.

PowerPC Platform n. A platform developed by IBM, Apple, and Motorola based on the 601 and later chips. This platform supports the use of multiple operating systems such as Mac OS, Windows NT, and AIX as well as software designed for those individual operating systems. Acronym: PPCP.

PowerPC Reference Platform n. An open system standard developed by IBM. IBM s goal in designing the PowerPC Reference Platform was to ensure compatibility among PowerPC systems built by different companies. Apple s PowerPC Macintoshes are not yet compliant with the PowerPC Reference Platform, but future versions are expected to be. Acronym: PReP. See also Common Hardware Reference Platform, open system, PowerPC.

PowerPoint n. Microsoft s presentation software. PowerPoint includes text-editing and graphics tools that can create slides for public presentations. The presentations can be printed, projected, displayed on a monitor, or, in the version included with Office 2000, saved and published as Web pages.

power supply n. An electrical device that transforms standard wall outlet electricity (115 120 VAC in the United States) into the lower voltages (typically 5 to 12 volts DC) required by computer systems. Personal computer power supplies are rated by wattage; they usually range from about 90 watts at the low end to 250 watts at the high end.

power surge n. See surge.

power up vb. To start up a computer; to begin a cold boot procedure; to turn on the power.

power user n. A person adept with computers, particularly on an applications-oriented level rather than on a programming level. A power user is someone who knows a considerable amount about computers and is comfortable enough with applications to be able to work with their most sophisticated features.

PPCP n. See PowerPC Platform.

PPM or ppm n. 1. Acronym for pages per minute. A rating of a printer s output capacity that is, the number of printed pages the printer can produce in one minute. A printer s PPM rating is usually provided by the manufacturer and is based on a normal page. Pages with excessive graphics or fonts may reduce a printer s PPM rate dramatically. 2. See pulse position modulation.

PPP n. Acronym for Point-to-Point Protocol. A widely used data link protocol for transmitting TCP/IP packets over dial-up telephone connections, such as between a computer and the Internet. PPP, which supports dynamic allocation of IP addresses, provides greater protection for data integrity and security and is easier to use than SLIP, at a cost of greater overhead. PPP itself is based on a Link Control Protocol (LCP) responsible for setting up a computer-to-computer link over telephone lines and a Network Control Protocol (NCP) responsible for negotiating network-layer details related to the transmission. It was developed by the Internet Engineering Task Force in 1991. Compare SLIP.

PPPoE n. Acronym for Point-to-Point Protocol over Ethernet. A specification for connecting users on an Ethernet network to the Internet through a broadband connection, such as a single DSL line, wireless device, or cable modem. Using PPPoE and a broadband modem, LAN users can gain individual authenticated access to high-speed data networks. By combining Ethernet and Point-to-Point Protocol (PPP), PPPoE provides Internet Service Providers (ISPs) with the ability to manipulate a limited number of IP addresses by assigning an address only when the user is connected to the Internet. PPPoE is an efficient way to create a separate connection for each user to a remote server. When the Internet connection is broken, the IP address becomes available to be assigned to another user.

PPS n. See peripheral power supply.

PPTP n. Acronym for Point-to-Point Tunneling Protocol. An extension of the Point-to-Point Protocol used for communications on the Internet. PPTP was developed by Microsoft to support virtual private networks (VPNs), which allow individuals and organizations to use the Internet as a secure means of communication. PPTP supports encapsulation of encrypted packets in secure wrappers that can be transmitted over a TCP/IP connection. See also virtual network.

PRAM n. Short for parameter RAM. A portion of RAM in Macintosh computers that contains configuration information such as the date and time, desktop pattern, and other control panel settings. See also RAM.

P-rating n. Short for performance rating. A microprocessor rating system by IBM, Cyrix, and others, based on throughput in realistic applications. Formerly, microprocessor clock speed was widely used as a method of rating, but it does not account for differing chip architectures or different types of work people do with computers. See also central processing unit, clock (definition 1), microprocessor.

precedence n. In applications, the order in which values in a mathematical expression are calculated. In general, application programs perform multiplication and division first, followed by addition and subtraction. Sets of parentheses can be placed around expressions to control the order in which they are calculated. See also operator associativity, operator precedence.

precision n. 1. The extent of detail used in expressing a number. For example, 3.14159265 gives more precision more detail about the value of pi than does 3.14. Precision is related to, but different from, accuracy. Precision indicates degree of detail; accuracy indicates correctness. The number 2.83845 is also more precise than 3.14, but it is less accurate for pi. Compare accuracy. 2. In programming, numeric values are often referred to as single-precision or double-precision values. The difference between the two is in the amount of storage space allotted to the value. See also double-precision, single-precision.

precompiler n. A program that reads in a source file and makes certain changes to prepare the source file for compilation. Also called: preprocessor. See also compiler (definition 2).

preemptive multitasking n. A form of multitasking in which the operating system periodically interrupts the execution of a program and passes control of the system to another waiting program. Preemptive multitasking prevents any one program from monopolizing the system. Also called: time-slice multitasking. See also multitasking. Compare cooperative multitasking.

Preferences n. A menu choice in many graphical user interface applications that allows the user to specify how the application will act each time it is used. For example, in a word processing application the user may be allowed to specify whether the ruler will appear, whether the document will appear in the same way as it will print (including margins), and other choices. Also called: Options, Prefs.

prefetch vb. Preloading buffering data for a streaming video clip before the clip begins playing. When prefetched data is stored on a computer, the video clip can be played without waiting for the initial buffering that usually occurs with streaming media. See also preroll.

prefix notation n. A form of algebraic notation, developed in 1929 by Jan Lukasiewicz, a Polish logician, in which the operators appear before the operands. For example, the expression (a + b) x (c d) would be written in prefix notation as x + a b c d. Also called: Polish notation. See also infix notation, postfix notation.

Prefs n. See Preferences.

Premiere n. Digital video editing software developed by Adobe Systems. The Premiere user interface uses command menus, windows, and floating pallets to make modifications to video clips. A timeline feature presents a graphic presentation of the length of the individual scenes and the order in which they appear. The editor can modify the edits and preview the results before exporting the file into one of several video formats.

PReP n. See PowerPC Reference Platform.

preprocessor n. A device or routine that performs preliminary operations on input before passing it on for further processing. See also front-end processor (definition 1). Compare postprocessor.

preroll vb. Data buffering that occurs before a streaming media clip plays. Preroll time varies depending on available bandwidth and the size of the file being buffered.

presence technology n. An application, such as instant messaging, which finds specific users when they are connected to the network and which may alert interested users to each other s presence. Third-generation wireless networks will integrate presence technology with digital cell phones, PDAs, pagers, and other communications and entertainment devices.

presentation broadcast n. A PowerPoint feature that allows you to run a presentation over the Web. The presentation is saved in HTML format and can contain audio and video. It can also be recorded and saved to be viewed later.

presentation graphics n. The representation of business information, such as sales figures and stock prices, in chart form rather than as lists of numbers. Presentation graphics are used to give viewers an immediate grasp of business statistics and their significance. Common examples are area charts, bar charts, line charts, and pie charts. Also called: business graphics.

presentation layer n. The sixth of the seven layers in the ISO/OSI reference model for standardizing computer-to-computer communications. The presentation layer is responsible for formatting information so that it can be displayed or printed. This task generally includes interpreting codes (such as tabs) related to presentation, but it can also include converting encryption and other codes and translating different character sets. See the illustration. See also ISO/OSI reference model.

Presentation layer.

Presentation Manager n. The graphical user interface provided with OS/2 versions 1.1 and later. The Presentation Manager derives from the MS-DOS based Windows environment and provides similar capabilities. The user sees a graphical, window-oriented interface, and the programmer uses a standard set of routines for handling screen, keyboard, mouse, and printer input and output, no matter what hardware is attached to the system. See also OS/2, Windows.

pressure-sensitive adj. Of or pertaining to a device in which pressing on a thin surface produces an electrical connection and causes an event to be registered by the computer. Pressure-sensitive devices include touch-sensitive drawing pens, membrane keyboards, and some touch screens. See also touch screen.

Pretty Good Privacy n. See PGP.

pretty print n. A feature of some editors used in programming that formats code so that it is easier to read and understand when printed. For example, a pretty-print feature might insert blank lines to set off modules or indent nested routines to make them easier to spot. See also code(definition 1), editor, module (definition 1), routine.

preventive maintenance n. Routine servicing of hardware intended to keep equipment in good operating condition and to find and correct problems before they develop into severe malfunctions.

preview n. In word processors and other applications, the feature that formats a document for printing but displays it on the video monitor rather than sending it directly to the printer.

PRI n. Acronym for Primary Rate Interface. One of two ISDN transmission rate services (the other is the basic rate interface, BRI). PRI has two variations. The first, which operates at 1.536 Mbps, transmits data over 23 B channels and sends signaling information at 64 Kbps over one D channel in the United States, Canada, and Japan. The second, which operates at 1.984 Mbps, transmits data over 30 B channels and sends signaling information at 64 Kbps over one D channel in Europe and Australia. See also BRI, ISDN.

primary channel n. The data-transmission channel in a communications device, such as a modem. Compare secondary channel.

Primary Domain Controller n. 1. In Windows NT, a database providing a centralized administration site for resources and user accounts. The database allows users to log onto the domain, rather than onto a specific host machine. A separate account database keeps track of the machines in the domain and allocates the domain s resources to users. 2. In any local area network, the server that maintains the master copy of the domain s user accounts database and that validates logon requests. Acronym: PDC.

primary key n. In databases, the key field that serves as the unique identifier of a specific tuple (row) in a relation (database table). Also called: major key. See also alternate key (definition 1), candidate key. Compare secondary key.

Primary Rate Interface n. See PRI.

primary storage n. Random access memory (RAM); the main general-purpose storage region to which the microprocessor has direct access. A computer s other storage options, such as disks and tape, are called secondary storage or (sometimes) backing storage.

primitive n. 1. In computer graphics, a shape, such as a line, circle, curve, or polygon, that can be drawn, stored, and manipulated as a discrete entity by a graphics program. A primitive is one of the elements from which a large graphic design is created. 2. In programming, a fundamental element in a language that can be used to create larger procedures that do the work a programmer wants to do.

print vb. In computing, to send information to a printer. The word is also sometimes used in the sense of show me or copy this. For example, the PRINT statement in Basic causes output to be displayed (printed) on the screen. Similarly, an application program that can be told to print a file to disk interprets the command as an instruction to route output to a disk file instead of to a printer.

print buffer n. A section of memory to which print output can be sent for temporary storage until the printer is ready to handle it. A print buffer can exist in a computer s random access memory (RAM), in the printer, in a separate unit between the computer and the printer, or on disk. Regardless of its location, the function of a print buffer is to free the computer for other tasks by taking print output at high speed from the computer and passing it along at the much slower rate required by the printer. Print buffers vary in sophistication: some simply hold the next few characters to be printed, and others can queue, reprint, or delete documents sent for printing.

printed circuit board n. A flat board made of nonconducting material, such as plastic or fiberglass, on which chips and other electronic components are mounted, usually in predrilled holes designed to hold them. The component holes are connected electrically by predefined conductive metal pathways that are printed on the surface of the board. The metal leads protruding from the electronic components are soldered to the conductive metal pathways to form a connection. A printed circuit board should be held by the edges and protected from dirt and static electricity to avoid damage. See the illustration. Acronym: PCB.

Printed circuit board.

printer n. A computer peripheral that puts text or a computer-generated image on paper or on another medium, such as a transparency film. Printers can be categorized in any of several ways: impact versus nonimpact; print technology; character formation; method of transmission; method of printing; print capability; and print quality.

• Impact versus nonimpact The most common distinction is impact versus nonimpact. Impact printers physically strike the paper and are exemplified by pin dot-matrix printers and daisy-wheel printers; nonimpact printers include every other type of print mechanism, including laser, ink-jet, and thermal printers.
• Print technology Chief among types of print technology are pin dot-matrix, ink-jet, laser, thermal, and (although somewhat outdated) daisy-wheel or thimble printers. Pin dot-matrix printers can be further classified by the number of pins in the print head: 9, 18, 24, and so on.
• Character formation Fully formed characters made of continuous lines (such as those produced by a daisy-wheel printer) versus dot-matrix characters composed of patterns of dots (such as those produced by standard dot-matrix, ink-jet, and thermal printers). Laser printers, while technically dot-matrix are generally considered to produce fully formed characters because their output is very clear and the dots are extremely small and closely spaced.
• Method of transmission Parallel (byte-by-byte transmission) versus serial (bit-by-bit transmission). These categories refer to the means by which output is sent to the printer rather than to any mechanical distinctions. Many printers are available in either parallel or serial versions, and still other printers offer both choices, yielding greater flexibility in installation options.
• Method of printing Character by character, line by line, or page by page. Character printers include standard dot-matrix, ink-jet, thermal, and daisy-wheel printers. Line printers include the band, chain, and drum printers that are commonly associated with large computer installations or networks. Page printers include the electrophotographic printers, such as laser printers.
• Print capability Text-only versus text-and-graphics. Text-only printers, including most daisy-wheel and thimble printers, and some dot-matrix and laser printers, can reproduce only characters for which they have matching patterns, such as embossed type or internal character maps. Text-and-graphics printers—dot matrix, ink-jet, laser, and others— can reproduce all manner of images by "drawing" each as a pattern of dots.
• Print quality Draft versus near-letter quality versus letter quality.

Printer Access Protocol n. See PAP (definition 2).

Printer Control Language n. A printer control language from Hewlett-Packard, used in its LaserJet, DeskJet, and RuggedWriter printer lines. Because of the LaserJet s dominance in the laser printer market, Printer Control Language has become a de facto standard. Acronym: PCL. Also called: Hewlett-Packard Printer Control Language.

printer controller n. The processing hardware in a printer, especially in a page printer. It includes the raster image processor, the memory, and any general-purpose microprocessors. A printer controller can also reside in a personal computer, attached via a high-speed cable to a printer that simply carries out its instructions. Compare printer engine.

printer driver n. A software program designed to enable other programs to work with a particular printer without concerning themselves with the specifics of the printer s hardware and internal language. Application programs can communicate properly with a variety of printers by using printer drivers, which handle all of the subtleties of each printer so that the application program doesn t have to. Today graphical user interfaces offer their own printer drivers, eliminating the need for an application that runs under the interface to have its own printer driver.

printer engine n. The part of a page printer, such as a laser printer, that actually performs the printing. Most printer engines are self-contained, replaceable cartridges. The engine is distinct from the printer controller, which includes all the processing hardware in the printer. The most widely used printer engines are manufactured by Canon. Compare printer controller.

printer file n. Output that would normally be destined for the printer but has been diverted to a computer file instead. A printer file is created for any of several reasons. For example, it allows output to be transferred to another program or to another computer. It also allows additional copies to be made at any time by simply copying the print image to the printer. Occasionally, the term printer file is used, incorrectly, to refer to the printer driver.

printer font n. A font residing in or intended for a printer. A printer font can be internal, downloaded, or on a font cartridge. Compare screen font.

Printer Job Language n. The printer command language developed by Hewlett-Packard that provides printer control at the print-job level. Using PJL commands, you can change default printer settings such as the number of copies to print. PJL commands also permit switching printer languages between print jobs without action by the user. If bi-directional communication is supported, a PJL-compatible printer can send information such as printer model and job status to the print server. Also called: Hewlett-Packard Printer Job Language. Acronym: PJL. See also page-description language, PostScript, Printer Control Language.

printer port n. A port through which a printer can be connected to a personal computer. On PC-compatible machines, printer ports are usually parallel ports and are identified in the operating system by the logical device name LPT. On many newer PCs, the parallel port on the case of the CPU has a printer icon beside it to identify it as a printer port. Serial ports can also be used for some printers (logical device name COM), although configuration is generally required. On Macintoshes, printer ports are usually serial ports and are also used to connect Macs to an AppleTalk network. See also AppleTalk, central processing unit, logical device, parallel port, serial port.

printer server n. See print server.

print head or printhead n. A component of an impact printer that contains the pins or other components that force ink from a ribbon onto paper.

printing pool n. Two or more identical printers that are connected to one print server and act as a single printer. In this case, when you print a document, the print job will be sent to the first available printer in the pool. See also print job, printer.

print job n. A single batch of characters printed as a unit. A print job usually consists of a single document, which can be one page or hundreds of pages long. To avoid having to print individual documents separately, some software can group multiple documents into a single print job. See also print spooler.

print mode n. A general term for the format of print output by a printer. Print modes range from portrait or landscape orientation of the paper to letter quality and size of the print. Dot-matrix printers support two print modes: draft and letter quality (LQ) or near-letter-quality (NLQ). Some printers can interpret both plain text (ASCII) and a page definition language such as PostScript. See also PostScript, printer.

printout n. See hard copy.

print quality n. The quality and clarity of characters produced by a printer. Print quality varies with the type of printer; in general, dot-matrix printers produce lower-quality output than laser printers. The printer mode can also affect quality. See also resolution (definition 1).

print queue n. A buffer for documents and images waiting to be printed. When an application places a document in a print queue, it is held in a special part of the computer s memory, where it waits until the printer is ready to receive it.

Print Screen key n. A key on IBM PC and compatible keyboards that normally causes the computer to send a character-based picture of the screen contents to the printer. The print screen feature works only when the display is in text mode or CGA graphics mode (the lowest-resolution color and graphics mode available on IBM compatibles). It will not work properly in other graphics modes. Some programs use the Print Screen key to capture a screen image and record it as a file on disk. These programs can typically work in any graphics mode and record the file as a graphics image. When the user is working directly with the MS-DOS operating system, and with some programs, the combination Control-Print Screen toggles the printer on or off. With printing turned on, the system sends every character to the printer as well as to the screen. The Print Screen key on the Apple Extended Keyboard is included for compatibility with operating systems such as MS-DOS. Also called: PrtSc key.

print server n. A workstation that is dedicated to managing printers on a network. The print server can be any station on the network. Also called: printer server.

Print Server for Macintosh n. An AppleTalk network integration service that enables computers running the Macintosh and Windows operating systems to share printers. Also called: MacPrint.

print spooler n. Computer software that intercepts a print job on its way to the printer and sends it to disk or memory instead, where the print job is held until the printer is ready for it. The term spooler is an acronym created from simultaneous peripheral operations on line.

print to file n. A command in many applications that instructs the program to format a document for printing and store the formatted document as a file rather than sending it to a printer.

print wheel n. See daisy wheel.

priority n. Precedence in receiving the attention of the microprocessor and the use of system resources. Within a computer, unseen and unnoticed levels of priority are the means by which many different types of potential clashes and disruptions are avoided. Similarly, tasks running on a computer can be assigned priorities that determine when and for how long they receive time from the microprocessor. On networks, stations can be assigned priorities that determine when and how often they can control the communications line, and messages can be assigned priorities that indicate how soon they must be transmitted. See also interrupt.

Priority Frame n. A telecommunications protocol developed by Infonet and Northern Telecom, Inc., designed to carry data, facsimile, and voice information.

privacy n. The concept that a user s data, such as stored files and e-mail, is not to be examined by anyone else without that user s permission. A right to privacy is not generally recognized on the Internet. Federal law protects only e-mail in transit or in temporary storage, and only against access by Federal agencies. Employers often claim a right to inspect any data on their systems. To obtain privacy, the user must take active measures such as encryption. See also encryption, PGP, Privacy Enhanced Mail. Compare security.

Privacy Enhanced Mail n. An Internet standard for e mail systems that use encryption techniques to ensure the privacy and security of messages. Acronym: PEM. See also encryption, standard. Compare PGP.

privacy policy n. Public statement delineating how a Web site uses the information it gathers from visitors to the site. Some Web sites sell this information to third parties or use the information for marketing purposes. Other sites have strict policies limiting how that information may be used.

private adj. A keyword used in some programming languages to signify that methods or variables can be accessed only by elements residing in the same class or module. See also class, keyword (definition 2), local variable, reserved word, scope. Compare public.

private assembly n. An assembly that is used by only one application. A private assembly is deployed into the directory structure of the application that uses it. Also called: private side-by-side assembly. See also shared assembly.

Private Branch Exchange n. See PBX.

private channel n. In Internet relay chat (IRC), a channel reserved for the use of a certain group of people. Private channel names are hidden from view by the public at large. Also called: secret channel. See also IRC.

Private Communications Technology n. See PCT (definition 2).

private folders n. In a shared network environment, those folders on a user s computer that are not accessible by other users on the network. Compare public folders.

private key n. One of two keys in public key encryption. The user keeps the private key secret and uses it to encrypt digital signatures and to decrypt received messages. See also public key encryption. Compare public key.

private line n. See dedicated line (definition 1).

Private Network-to-Network Interface n. See PNNI.

privatization n. Generally, the process of turning something over from government to commercial industry control. In the context of computer science and the Internet, the term refers to the government s turning over of various Internet backbones to private industry for example, control of NSFnet was passed from the government to private business in 1992 and to the government s more recent (1998) privatization of responsibility for domain names and addresses, which was shifted from IANA and NSI/InterNIC to a new organization known as ICANN. See also IANA, ICANN, InterNIC.

privileged instruction n. An instruction (usually a machine instruction) that can be executed only by the operating system. Privileged instructions exist because the operating system needs to perform certain operations that applications should not be allowed to perform; therefore, only the operating-system routines have the necessary privilege to execute these particular instructions.

privileged mode n. A mode of execution, supported by the protected mode of the Intel 80286 and higher microprocessors, in which software can carry out restricted operations that manipulate critical components of the system, such as memory and input/output ports (channels). Application programs cannot be executed in privileged mode; the heart (kernel) of the OS/2 operating system can be, as can the programs (device drivers) that control devices attached to the system.

privileges n. See access privileges.

PRN n. The logical device name for printer. A name reserved by the MS-DOS operating system for the standard print device. PRN usually refers to a system s first parallel port, also known as LPT1.

.pro n. One of seven new top-level domain names approved in 2000 by the Internet Corporation for Assigned Names and Numbers (ICANN), .pro is meant for use in Web sites relating to professions such as physicians, accountants, and lawyers. Six of the new domains became available for use in the spring of 2001; negotiations are still underway for the final registry agreement for the .pro domain.

probability n. The likelihood that an event will happen, which can often be estimated mathematically. In mathematics, statistics and probability theory are related fields. In computing, probability is used to determine the likelihood of failure or error in a system or device.

problem solving n. 1. The process of devising and implementing a strategy for finding a solution or for transforming a less desirable condition into a more desirable one. 2. An aspect of artificial intelligence wherein the task of problem solving is performed solely by a program. See also artificial intelligence.

procedural language n. A programming language in which the basic programming element is the procedure (a named sequence of statements, such as a routine, subroutine, or function). The most widely used high-level languages (C, Pascal, Basic, FORTRAN, COBOL, Ada) are all procedural languages. See also procedure. Compare nonprocedural language.

procedural rendering n. The rendering of a two-dimensional image from three-dimensional coordinates with texturing according to user-specified conditions, such as direction and degree of lighting.

procedure n. In a program, a named sequence of statements, often with associated constants, data types, and variables, that usually performs a single task. A procedure can usually be called (executed) by other procedures, as well as by the main body of the program. Some languages distinguish between a procedure and a function, with the latter (the function) returning a value. See also function, parameter, procedural language, routine, subroutine.

procedure call n. In programming, an instruction that causes a procedure to be executed. A procedure call can be located in another procedure or in the main body of the program. See also procedure.

process¹ n. A program or part of a program; a coherent sequence of steps undertaken by a program.

process² vb. To manipulate data with a program.

process-bound adj. Limited in performance by processing requirements. See also computation-bound.

process color n. A method of handling color in a document in which each block of color is separated into its subtractive primary color components for printing: cyan, magenta, and yellow (as well as black). All other colors are created by blending layers of various sizes of halftone spots printed in cyan, magenta, and yellow to create the image. See also color model, color separation (definition 1). Compare spot color.

processing n. The manipulation of data within a computer system. Processing is the vital step between receiving data (input) and producing results (output) the task for which computers are designed.

processor n. See central processing unit, microprocessor.

Processor Direct Slot n. See PDS (definition 1).

Processor Input/Output n. See PIO.

Procmail n. An open-source e-mail-processing utility for Linux and other UNIX-based computers and networks. Procmail can be used to create mail servers and mailing lists, filter mail, sort incoming mail, preprocess mail, and perform other mail-related functions.

Prodigy n. An Internet service provider (ISP) that offers Internet access and a wide range of related services. Prodigy was founded by IBM and Sears as a proprietary online service, was acquired by International Wireless in 1996, and in 1999 entered into a partnership with SBC Communications. The addition of SBC s Internet customer base made Prodigy the third largest ISP in the United States.

Prodigy Information Service n. An online information service founded by IBM and Sears. Like its competitors America Online and CompuServe, Prodigy offers access to databases and file libraries, online chat, special interest groups, e-mail, and Internet connectivity. Also called: Prodigy.

product n. 1. An operator in the relational algebra used in database management that, when applied to two existing relations (tables), results in the creation of a new table containing all possible ordered concatenations (combinations) of tuples (rows) from the first relation with tuples from the second. The number of rows in the resulting relation is the product of the number of rows in the two source relations. Also called: Cartesian product. Compare inner join. 2. In mathematics, the result of multiplying two or more numbers. 3. In the most general sense, an entity conceived and developed for the purpose of competing in a commercial market. Although computers are products, the term is more commonly applied to software, peripherals, and accessories in the computing arena.

production system n. In expert systems, an approach to problem solving based on an IF this, THEN that approach that uses a set of rules, a database of information, and a rule interpreter to match premises with facts and form a conclusion. Production systems are also known as rule-based systems or inference systems. See also expert system.

Professional Graphics Adapter n. A video adapter introduced by IBM, primarily for CAD applications. The Professional Graphics Adapter is capable of displaying 256 colors, with a horizontal resolution of 640 pixels and a vertical resolution of 480 pixels. Acronym: PGA.

Professional Graphics Display n. An analog display introduced by IBM, intended for use with their Professional Graphics Adapter. See also Professional Graphics Adapter.

profile¹ n. See user profile.

profile² vb. To analyze a program to determine how much time is spent in different parts of the program during execution.

profiler n. A diagnostic tool for analyzing the run-time behavior of programs.

Profiles for Open Systems Internetworking Technology n. See POSIT.

program¹ n. A sequence of instructions that can be executed by a computer. The term can refer to the original source code or to the executable (machine language) version. Also called: software. See also program creation, routine, statement.

program² vb. To create a computer program, a set of instructions that a computer or other device executes to perform a series of actions or a particular type of work.

program button n. On a handheld device, a navigation control that is pressed to launch an application. Also called: application button.

program card n. See PC Card, ROM card.

program cartridge n. See ROM cartridge.

program comprehension tool n. A software engineering tool that facilitates the process of understanding the structure and/or functionality of computer applications. Acronym: PCT. Also called: software exploration tool.

program counter n. A register (small, high-speed memory circuit within a microprocessor) that contains the address (location) of the instruction to be executed next in the program sequence.

program creation n. The process of producing an executable file. Traditionally, program creation comprises three steps: (1) compiling the high-level source code into assembly language source code; (2) assembling the assembly language source code into machine-code object files; and (3) linking the machine-code object files with various data files, run-time files, and library files into an executable file. Some compilers go directly from high-level source to machine-code object, and some integrated development environments compress all three steps into a single command. See also assembler, compiler (definition 2), linker, program.

program encapsulation n. A method of dealing with programs with Year 2000 problems that entailed modifying the data with which a program worked. The input data is modified to reflect a parallel date in the past that the program can handle. When output is generated, that data is changed again, to reflect the correct date. The program itself remains unchanged.

program file n. A disk file that contains the executable portions of a computer program. Depending on its size and complexity, an application or other program, such as an operating system, can be stored in several different files, each containing the instructions necessary for some part of the program s overall functioning. Compare document file.

program generator n. A program that creates other programs (usually in source code) based on a set of specifications and relationships given by the user. Program generators are often used to simplify the task of creating an application. See also 4GL, application generator.

program listing n. A copy, usually on paper, of the source code of a program. Some compilers can generate program listings with line numbers, cross-references, and so on.

program logic n. The logic behind the design and construction of a program that is, the reasons it works the way it does. See also logic error.

programmable adj. Capable of accepting instructions for performing a task or an operation. Being programmable is a characteristic of computers.

programmable function key n. Any of several, sometimes unlabeled, keys on some third-party keyboards that allow the user to play back previously stored key combinations or sequences of keystrokes called macros. The same effect can be achieved with a standard keyboard and a keyboard enhancer, the latter of which intercepts the keyboard codes and substitutes modified values; but programmable function keys accomplish this without requiring RAM-resident software. Compare keyboard enhancer.

programmable interrupt controller n. An Intel chip that handles interrupt requests (IRQs). IBM AT machines use two programmable interrupt controllers to accommodate a maximum of 15 IRQs. The programmable interrupt controller has been replaced by the advanced programmable interrupt controller (APIC), which supports multiprocessing. Acronym: PIC. See also IBM AT, IRQ.

programmable logic array n. See field-programmable logic array.

programmable logic device n. A logic chip that is programmed by the customer rather than by the manufacturer. Like a gate array, a programmable logic device consists of a collection of logic gates; unlike a gate array, a programmable logic device need not have its programming completed as part of the manufacturing process. Acronym: PLD. See also logic chip. Compare gate array.

programmable read-only memory n. See PROM.

program maintenance n. The process of supporting, debugging, and upgrading a program in response to feedback from individual or corporate users or the marketplace in general.

programmatic interface n. 1. A user interface dependent on user commands or on a special programming language, as contrasted with a graphical user interface. UNIX and MS-DOS have programmatic interfaces; the Apple Macintosh and Microsoft Windows have graphical user interfaces. See also command-line interface, graphical user interface, iconic interface. 2. The set of functions any operating system makes available to a programmer developing an application. See also application programming interface.

Programmed Input/Output n. See PIO.

Programmed Inquiry, Learning or Teaching n. See PILOT.

programmer n. 1. An individual who writes and debugs computer programs. Depending on the size of the project and the work environment, a programmer might work alone or as part of a team, be involved in part or all of the process from design through completion, or write all or a portion of the program. See also program. 2. In hardware, a device used to program read-only memory chips. See also PROM, ROM (definition 2).

programmer s switch n. A pair of buttons on Macintosh computers that enable the user to reboot the system or to enter a command-line interface at a low level of the operating system. Originally, only programmers testing software were expected to need those functions, so early models of the Macintosh hid the buttons inside the cabinet and supplied a plastic clip that could be attached so that the programmer could push them. In many later models the buttons are built into the cabinet; the button to reboot the system is marked with a triangle pointing leftward, and the other button is marked with a circle.

programming n. The art and science of creating computer programs. Programming begins with knowledge of one or more programming languages, such as Basic, C, Pascal, or assembly language. Knowledge of a language alone does not make a good program. Much more can be involved, such as expertise in the theory of algorithms, user interface design, and characteristics of hardware devices. Computers are rigorously logical machines, and programming requires a similarly logical approach to designing, writing (coding), testing, and debugging a program. Low-level languages, such as assembly language, also require familiarity with the capabilities of a microprocessor and the basic instructions built into it. In the modular approach advocated by many programmers, a project is broken into smaller, more manageable modules stand-alone functional units that can be designed, written, tested, and debugged separately before being incorporated into the larger program. See also algorithm, kludge (definition 2), modular design, object-oriented programming, spaghetti code, structured programming.

programming language n. Any artificial language that can be used to define a sequence of instructions that can ultimately be processed and executed by the computer. Defining what is or is not a programming language can be tricky, but general usage implies that the translation process from the source code expressed using the programming language to the machine code that the computer needs to work with be automated by means of another program, such as a compiler. Thus, English and other natural languages are ruled out, although some subsets of English are used and understood by some fourth-generation languages. See also 4GL, compiler (definition 2), natural language, program.

Programming Language I n. See PL/I.

program specification n. In software development, a statement of the goals and requirements of a project, as well as the relation of the project to other projects.

program state n. The condition of a program (stack contents, memory contents, instruction being executed) at a given moment.

program statement n. The statement defining the name, briefly describing the operation, and possibly giving other information about a program. Some languages, such as Pascal, have an explicit program statement; others do not, or they use other forms (such as the main( ) function in C).

progressive JPEG n. An enhancement to the JPEG graphics file format that gradually displays a photo-realistic picture in a Web browser, showing increasingly detailed versions of the picture until the entire file has finished downloading.

progressive scanning n. 1. A display technique used on computer monitors in which the image is created, line by line, in a single top-to-bottom sweep of the electron gun. The resulting image is of higher quality than is possible with the interlace scanning used for television sets. Progressive scanning might be used on next-generation digital television equipment. It does, however, require twice the signal bandwidth of interlace scanning. Compare interlace scanning. 2. A line-by-line (rather than every-other-line) technique used with some video cameras to capture images of moving objects. Such cameras are used primarily for tasks such as monitoring assembly lines and traffic flow.

project n. An operator in the relational algebra used in database management. Given relation (table) A, the project operator builds a new relation containing only a specified set of attributes (columns) of A.

Project 802 n. The IEEE project to define networking standards that resulted in the 802.x specifications. See also IEEE, IEEE 802.x.

Project Gutenberg n. A project that makes the texts of books that are in the public domain available over the Internet. The files for the books are in plain ASCII, to make them accessible to as many people as possible. Project Gutenberg, based at the University of Illinois at Urbana-Champaign, can be reached at mrcnext.cso.uiuc.edu via FTP or through the Web page http://www.promo.net/pg/. See also ASCII.

projection-join normal form n. See normal form (definition 1).

project life cycle n. A sequence of preplanned stages for taking a project from beginning to end.

project management n. The process of planning, monitoring, and controlling the course and development of a particular undertaking.

Prolog n. Short for Programming in Logic. A language designed for logic programming. Prolog evolved during the 1970s in Europe (primarily France and Scotland), and the first Prolog compiler was developed in 1972 by Philippe Roussel, at the University of Marseilles. The language has subsequently attained wide use in the field of artificial intelligence. Prolog is a compiled language that works with the logical relationship between pieces of data rather than mathematical relationships. See also artificial intelligence.

PROM n. Acronym for programmable read-only memory. A type of read-only memory (ROM) that allows data to be written into the device with hardware called a PROM programmer. After a PROM has been programmed, it is dedicated to that data, and it cannot be reprogrammed. See also EEPROM, EPROM, ROM (definition 2).

PROM blaster n. See PROM programmer.

PROM blower n. See PROM programmer.

promiscuous-mode transfer n. In network communications, a transfer of data in which a node accepts all packets regardless of their destination address.

PROM programmer n. A hardware device that records instructions or data on a PROM (programmable read-only memory) chip or an EPROM (erasable programmable read-only memory) chip. Also called: PROM blaster, PROM blower. See also EPROM, PROM.

prompt n. 1. In command-driven systems, one or more symbols that indicate where users are to enter commands. For instance, in MS-DOS, the prompt is generally a drive letter followed by a greater than symbol (C>). In UNIX, it is usually %. See also command-driven system, DOS prompt. 2. Displayed text indicating that a computer program is waiting for input from the user.

propagated error n. An error used as input to another operation, thus producing another error.

propagation n. Travel of a signal, such as an Internet packet, from its source to one or more destinations. Propagation of messages over different paths with different lengths can cause messages to appear at a user s computer with varying delivery times. See also propagation delay.

propagation delay n. The time needed by a communications signal to travel between two points; in satellite links, a noticeable delay of between one-quarter second and one-half second, caused by the signal traveling through space.

propeller head n. Slang for a person who is obsessed with computers or other technology; a geek. The name refers to a child s beanie cap topped by a spinning propeller.

property n. In Windows 9x, a characteristic or parameter of an object or device. Properties of a file, for example, include type, size, and creation date and can be identified by accessing the file s property sheet. See also property sheet.

property sheet n. A type of dialog box in Windows 9x, accessed by choosing Properties in the File menu or by right-clicking on an object and selecting Properties, that lists the attributes or settings of an object such as a file, application, or hardware device. A property sheet presents the user with a tabbed, index-card-like selection of property pages, each of which features standard dialog-style controls for customizing parameters.

proportional font n. A set of characters in a particular style and size in which a variable amount of horizontal space is allotted to each letter or number. In a proportional font, the letter i, for example, is allowed less space than the letter m. Compare monospace font.

proportional spacing n. A form of character spacing in which the horizontal space each character occupies is proportional to the width of the character. The letter w, for example, takes up more space than the letter i. Compare monospacing.

proprietary adj. Of, pertaining to, or characteristic of something that is privately owned. Generally, the term refers to technology that has been developed by a particular corporation or entity, with specifications that are considered by the owner to be trade secrets. Proprietary technology may be legally used only by a person or entity purchasing an explicit license. Also, other companies are unable to duplicate the technology, both legally and because its specifications have not been divulged by the owner. Compare public domain.

proprietary software n. A program owned or copyrighted by an individual or a business and available for use only through purchase or by permission of the owner. Compare open source, public-domain software.

protected n. A keyword in a programming language (such as Java or C++) used in a method or variable declaration. It signifies that the method or variable can be accessed only by elements residing in its class, subclasses, or classes in the same package. See also class, declaration, method, package, variable.

protected mode n. An operating mode of the Intel 80286 and higher microprocessors that supports larger address spaces and more advanced features than real mode. When started in protected mode, these CPUs provide hardware support for multitasking, data security, and virtual memory. The Windows (version 3.0 and later) and OS/2 operating systems run in protected mode, as do most versions of UNIX for these microprocessors. Compare real mode.

protocol n. See communications protocol.

protocol analyzer n. A management tool designed to identify and diagnose computer network problems. A protocol analyzer looks at LAN (local area network) or WAN (wide area network) traffic and finds protocol errors, connection delays, and other network faults. The protocol analyzer can filter and decode traffic, suggest solutions to problems, provide graphical reports, and show traffic by protocol and percent utilization. See also communications protocol.

protocol layer n. See layer.

protocol stack n. The set of protocols that work together on different levels to enable communication on a network. For example, TCP/IP, the protocol stack on the Internet, incorporates more than 100 standards including FTP, IP, SMTP, TCP, and Telnet. See also ISO/OSI reference model. Compare protocol suite.

protocol suite n. A set of protocols designed, usually by one vendor, as complementary parts of a protocol stack. Compare protocol stack.

prototyping n. The creation of a working model of a new computer system or program for testing and refinement. Prototyping is used in the development of both new hardware and software systems and new systems of information management. Tools used in the former include both hardware and support software; tools used in the latter can include databases, screen mockups, and simulations that, in some cases, can be developed into a final product.

proxy n. A computer (or the software that runs on it) that acts as a barrier between a network and the Internet by presenting only a single network address to external sites. By acting as a go-between representing all internal computers, the proxy protects network identities while still providing access to the Internet. See also proxy server.

proxy server n. A firewall component that manages Internet traffic to and from a local area network (LAN) and can provide other features, such as document caching and access control. A proxy server can improve performance by supplying frequently requested data, such as a popular Web page, and can filter and discard requests that the owner does not consider appropriate, such as requests for unauthorized access to proprietary files. See also firewall.

PrtSc key n. See Print Screen key.

.ps n. The file extension that identifies PostScript printer files. See also PostScript.

PS/2 bus n. See Micro Channel Architecture.

PSD n. A graphics file format used to create, modify, and display still images in Photoshop, a software application designed by Adobe Systems. PSD files have a file extension of .psd.

PSE n. See Packet Switching Exchange.

psec n. See picosecond.

pseudocode n. 1. A machine language for a nonexistent processor (a pseudomachine). Such code is executed by a software interpreter. The major advantage of p-code is that it is portable to all computers for which a p-code interpreter exists. The p-code approach has been tried several times in the microcomputer industry, with mixed success. The best known attempt was the UCSD p-System. Abbreviation: p-code. See also pseudomachine, UCSD p-System. 2. Any informal, transparent notation in which a program or algorithm description is written. Many programmers write their programs first in a pseudocode that looks much like a mixture of English and their favorite programming language, such as C or Pascal, and then translate it line by line into the actual language being used.

pseudo compiler n. A compiler that generates a pseudolanguage. See also pseudolanguage.

pseudocomputer n. See pseudomachine.

pseudolanguage n. A nonexistent programming language that is, one for which no implementation exists. The term can refer either to the machine language for a nonexistent processor or to a high-level language for which no compiler exists. See also pseudocode.

pseudomachine n. A processor that doesn t actually exist in hardware but that is emulated in software. A program written for the pseudomachine can run on several platforms without having to be recompiled. Abbreviation: p-machine. See also pseudocode, UCSD p-System.

pseudo-op n. See pseudo-operation.

pseudo-operation n. In programming, a program instruction that conveys information to an assembler or compiler but is not translated into a machine language instruction for example, an instruction that establishes the value of a constant or the manner in which Boolean (logical) expressions are to be evaluated.Abbreviation: pseudo-op.

pseudo-streaming n. A method used for real-time display of audio and video over the Web. Unlike sound or video files that are downloaded to a computer in their entirety before they can be played back, pseudo-streaming enables playback after only a portion of the file enough to fill a buffer on the receiving computer has been downloaded. Pseudo-streaming, unlike true, or Web, streaming, does not depend on server software to dynamically monitor the transmission. It can, however, play back only from the beginning of the file, rather than from any point, as can be the case with true streaming. See also stream.

PSK n. See phase-shift keying.

PSN n. Acronym for packet-switching network. See packet switching.

PSTN n. See Public Switched Telephone Network.

p-system n. An operating system based on a pseudomachine implemented in software. A program written for the p-system is more portable than one written for a machine-dependent operating system. See also UCSD p-System.

P-type semiconductor n. Semiconductor material in which electrical conduction is carried by holes ( vacancies left by electrons). Whether a semiconductor is N-type or P-type depends on the kind of dopant added during manufacture. A dopant with a shortage of electrons results in a P-type semiconductor. Compare N-type semiconductor.

pub n. See /pub.

/pub n. Short for public. A directory in an anonymous FTP archive that is accessible by the public and that generally contains files available for free download. See also anonymous FTP.

public adj. A keyword in some programming languages to signify that methods or variables can be accessed by elements residing in other classes or modules. See also class, keyword (definition 2), global variable, reserved word, scope. Compare private.

public directory n. A directory on an FTP server that is accessible by anonymous users for the purpose of retrieving or storing files. Often the directory is called /pub. See also anonymous FTP, FTP (definition 1), FTP server /pub.

public domain n. The set of all creative works, such as books, music, or software, that are not covered by copyright or other property protection. Works in the public domain can be freely copied, modified, and otherwise used in any manner for any purpose. Much of the information, texts, and software on the Internet is in the public domain, but putting a copyrighted work on the Internet does not put it in the public domain. Compare proprietary.

public-domain software n. A program donated for public use by its owner or developer and freely available for copying and distribution. Compare free software, freeware, proprietary software, shareware.

public files n. Files with no access restrictions.

public folders n. The folders that are made accessible on a particular machine or by a particular user in a shared networking environment. Compare private folders.

public key n. One of two keys in public key encryption. The user releases this key to the public, who can use it for encrypting messages to be sent to the user and for decrypting the user s digital signature. See also public key encryption. Compare private key.

public key cryptography n. See public key encryption.

public key encryption n. An asymmetric scheme that uses a pair of keys for encryption: the public key encrypts data, and a corresponding secret key decrypts it. For digital signatures, the process is reversed: the sender uses the secret key to create a unique electronic number that can be read by anyone possessing the corresponding public key, which verifies that the message is truly from the sender. See also private key, public key.

public rights n. In the context of the Internet, the extent to which members of the public are permitted to use (and to place) information on the Internet under intellectual property law. See also fair use, public domain, public-domain software.

Public Switched Telephone Network n. The public telephone system.

Publisher n. A software application developed by Microsoft Corporation to help businesses create high-quality marketing and business material. A part of the Office product family, Publisher provides business users with design options for a variety of publications, such as newsletters, flyers, brochures, and Web pages.

publishing point n. A publishing point is a virtual directory used for storing content or delivering a live stream. End users reach a publishing point through its URL. There are two types of unicast publishing points: on-demand for stored content and broadcast for live streams. See also on-demand publishing point, broadcast publishing point. Compare unicast.

puck n. A pointing device used with a graphics tablet. A puck, which is often used in engineering applications, is a mouselike device with buttons for selecting items or choosing commands and a clear plastic section extending from one end with cross hairs printed on it. The intersection of the cross hairs on the puck points to a location on the graphics tablet, which in turn is mapped to a specific location on the screen. Because the puck s cross hairs are on a transparent surface, a user can easily trace a drawing by placing it between the graphics tablet and the puck and moving the cross hairs over the lines of the drawing. See also graphics tablet, stylus.

Puck.

puff and sip device n. An assistive computer technology for people with mobility impairments. A puff and sip device is a head-mounted alternative to using a mouse or keyboard. For mouse functionality, the device allows a user to move the mouse pointer without using his or her hands by puffing air into a tube.

pull vb. The process of retrieving data from a network server. See pop. Compare push (definition 2).

pull-down menu n. A menu that is pulled down from the menu bar and that remains available as long as the user holds it open. Compare drop-down menu.

pulse n. A transient signal, usually brief and with a discrete onset and offset.

pulse amplitude modulation n. A method of encoding information in a signal by varying the amplitude of pulses. The unmodulated signal consists of a continuous train of pulses of constant frequency, duration, and amplitude. During modulation the pulse amplitudes are changed to reflect the information being encoded. See the illustration. Acronym: PAM. Compare pulse code modulation, pulse duration modulation, pulse position modulation.

Pulse amplitude modulation.

pulse code modulation n. A method of encoding information in a signal by varying the amplitude of pulses. Unlike pulse amplitude modulation (PAM), in which pulse amplitude can vary continuously, pulse code modulation limits pulse amplitudes to several predefined values. Because the signal is discrete, or digital, rather than analog, pulse code modulation is more immune to noise than PAM. Acronym: PCM. Compare pulse amplitude modulation, pulse duration modulation, pulse position modulation.

pulse dialing n. See rotary dialing.

pulse duration modulation n. A method of encoding information in a signal by varying the duration of pulses. The unmodulated signal consists of a continuous train of pulses of constant frequency, duration, and amplitude. During modulation, the pulse durations are changed to reflect the information being encoded. See the illustration. Acronym: PDM. Also called: pulse length modulation, pulse width modulation.

Pulse duration modulation.

pulse length modulation n. See pulse duration modulation.

pulse position modulation n. A method of encoding information in a signal by varying the position of pulses. The unmodulated signal consists of a continuous train of pulses of constant frequency, duration, and amplitude. During modulation, the pulse positions are changed to reflect the information being encoded. See the illustration. Acronym: PPM. Compare pulse amplitude modulation, pulse code modulation, pulse duration modulation.

Pulse position modulation.

pulse width modulation n. See pulse duration modulation.

punched card n. An outdated computer-input medium made of stiff paper that stores data bits in columns containing patterns of punched holes. The method for creating the patterns used for different byte values is called Hollerith coding. See also Hollerith tabulating/recording machine.

punched-card reader n. See card reader.

pure procedure n. Any procedure that modifies only data that is dynamically allocated (usually on the stack). A pure procedure cannot modify either global data or its own code. This restriction allows a pure procedure to be called simultaneously by separate tasks. See also reentrant code.

purge vb. To eliminate old or unneeded information systematically; to clean up, as files.

push¹ n. A technology developed in relation to the World Wide Web, designed to provide end users with personalized Web access by having a site actively push requested information to the user s desktop, either automatically or at specified intervals. Push was developed as a means of relieving users from having to actively retrieve ( pull ) information from the Web. It is not, as yet, especially popular.

push² vb. 1. To add a new element to a stack, a data structure generally used to temporarily hold pieces of data being transferred or the partial result of an arithmetic operation. See also stack. Compare pop. 2. In networks and the Internet, to send data or a program from a server to a client at the instigation of the server. See also push². Compare pull.

put vb. In programming, to write data, typically to a file; in particular, to write a very small unit of data, such as a character.

PVC n. Acronym for permanent virtual circuit. A permanent logical connection between two nodes on a packet-switching network. The PVC appears as a dedicated line to the nodes, but the data can be transmitted on a common carrier. See also common carrier, node (definition 2 ), packet switching, virtual private network. Compare SVC.

pwd n. Acronym for print working directory. The UNIX command for displaying the current directory.

PWM n. Acronym for pulse width modulation. See pulse duration modulation.

PXE boot n. Acronym for Preboot Execution Environment boot. A BIOS-supported technology used to boot a PC remotely. To power on a PC and boot it from the network, PXE must be enabled in the BIOS, and the NIC in the PC must be PXE compliant. PXE boot is specified in the Intel Wired for Management (WfM) standard. Also called: network boot.

pyramid diagram n. A diagram that is used to show foundation-based relationships.

Python n. A portable, interpreted, object-oriented programming language developed and freely distributed by its developer. Python runs on many platforms, including UNIX, Windows, OS/2, and Macintosh, and is used for writing TCP/IP applications.