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- physical medium attachment sublayer (PMA sublayer):
- In a local area network, that portion of the physical layer implemented by the functional circuitry of the medium attachment unit. (Figure 39 - Example of a protocol structure for a LAN).
- physical record:
- A record that is stored as contiguous data on a data medium or is moved as a block in a transmission medium.
- physical recording density:
- The number of flux transitions recorded on a track per unit of length or of angle. Usually, the units used are flux transitions per millimeter (ftpmm) for length, and flux transitions per radian (ftprad) for angles.
- physical schema:
- The part of the database schema that pertains to the physical level.
- physical security:
- Protection of people or property by means such as barriers, locks, and guards.
- physical signaling sublayer (PLS sublayer):
- In a local area network, that portion of the physical layer that interfaces with the medium access control sublayer and performs bit symbol encoding and transmission, bit symbol reception and decoding, and optional isolation functions. (Figure 39 - Example of a protocol structure for a LAN).
- physical track group:
- A fixed number of consecutive physical tracks in the user data area.
- pick device:
- An input unit used to specify one or more display elements; for example, a lightpen.
- pictogram:
- Synonym for icon.
- pictorial block:
- One of a predefined set of characters that can be used to form simple graphics.
- pictorial character:
- One of a predefined set of characters that can be used to form simple graphics such as rulings, boxes, figures, logos, or diagrams.
- picture:
- In programming languages, a language construct that describes the format of string-type data objects by means of a model character literal.
- picture cell:
- Synonym for pel.
- picture element:
- Synonym for pixel.
- picture processing:
- Synonym for image processing.
- piggyback entry:
- Unauthorized access to a data processing system via an authorized user's legitimate connection.
- pilot project:
- A project designed to test a preliminary version of an information processing system under actual but limited operating conditions.
- pincushion distortion:
- A distortion such that the image of a scene appears to bulge inward on all sides like a pincushion. The distortion may be caused by an increase in effective magnification as points in the image move away from the image center.
- pipeline:
- A sequence of process segments that are handled by successive processors or tasks that may execute in parallel. The concept of pipeline may be applied at
- the macrolevel, such as in a communication switch that supports concurrent processing of input, routing, and output, or
- the microlevel, such as within a central processing unit where each instruction may be handled by instruction fetch, data fetch, arithmetic or logic operation, and data store processes.
- pipeline processing:
- The operating mode that uses one or more pipelines.
- pipeline processor:
- A processor in which instruction execution takes place in stages in a series of units, arranged in such a way that several units can simultaneously process the appropriate parts of several instructions.
- pitch:
- The unvarying width of the escapement of all graphic characters in a given monospaced font.
- pixel:
- The smallest element of a display surface that can be independently assigned attributes such as color and intensity. Synonymous with picture element.
- pixel group processing:
- An image-processing technique in which each pixel is processed together with its adjacent pixels; for example: the weighted averaging of pixel arrays used to facilitate spatial filtering.
- pixel map:
- A two-dimensional array of pixel values. Synonymous with pixmap.
- pixel point processing:
- An image-processing technique in which image contrast is adjusted by multiplying or dividing individual pixels by a constant, or image brightness is adjusted by adding or subtracting a constant value from individual pixels.
- pixel value:
- A discrete value that represents color, intensity, and other attributes of a pixel.
- pixmap:
- Synonym for pixel map.
- PL/I:
- A general-purpose, high-level, procedure-oriented language that has characteristics of Fortran, COBOL, and ALGOL. The name is derived from programming language one, and is pronounced "pe'el-wun".
- PLA:
- programmable logic array.
- place-holder node:
- A hypermedia node that may contain its title, its unique identifier, and a brief description of the data that will be associated with it. Place-holder nodes are used during detailed design.
- plaintext:
- Data, the semantic content of which is available without using cryptographic techniques. Synonymous with cleartext.
- plasma panel:
- That part of a display device which consists of a grid of electrodes in a flat, gas-filled panel. The display image can persist for a long time without refresh. Synonymous with gas panel.
- playback:
- In program development, a technique in which a history of execution of all or part of a program is recorded in such a manner that the input and output can be regenerated under the user's control, perhaps in either the forward or backward direction. Playback is used in debugging.
- plotter:
- An output unit that produces a hard copy record of data in the form of a two-dimensional graphic representation.
- plotting head:
- The part of a plotter used to create marks on a display surface.
- PLS sublayer:
- physical signaling sublayer.
- plug-in:
- (1) In networking, an extension to a browser for handling special types of data. (2) A small software program that is attached to a larger application to provide additional functionality.
- PM:
- phase modulation.
- PMA sublayer:
- physical medium attachment sublayer.
- pneumatic glove:
- A glove output device with layers of strategically placed air bladders that are rapidly inflated and deflated. Synonymous with pneumatic tactile glove.
- pneumatic tactile glove:
- Synonym for pneumatic glove.
- pocket:
- A card stacker in a card sorter.
- pocket calculator:
- A calculator, capable of operating independently of electric power lines, that is sufficiently light in weight and small in size to be operated in the hand or carried in a pocket. Synonymous with hand-held calculator.
- pod:
- A capsule or a booth that encloses a participant in a virtual world.
- pointer:
- (1) In organization of data, a data element that indicates the location of another data element. (2) In programming languages, a data object whose data value is the address of another data object. (3) In computer
graphics, a symbol displayed on a screen that a user can move with a pointing device, such as a mouse, to select items, and that may change shape with context.
- pointer type:
- A data type, each data object of which is a pointer. Synonymous with accesss type.
- pointing device:
- An instrument used to move an aiming symbol on a screen; for example: a mouse, a trackball, or a joystick.
- pointing stick:
- A pointing device, resembling the eraser at the tip of a pencil, usually placed in the middle of a keyboard of some portable computers.
- point of presence (POP):
- A place at which a user gains access into the Internet. Internet service providers may have points of presence in many cities.
- point-of-sale device:
- A device for recording sales data on machine-readable media at the time each sale is made.
- point-to-point connection:
- A connection established between two data stations.
- Point-to-Point Protocol (PPP):
- The protocol for transmitting network layer datagrams (such as IP packets) over serial point-to-point links via dial-up telephone. PPP provides greater protection for data integrity and security than does SLIP, but with a greater overhead. Contrast with Serial Line Internet Protocol.
- point transformation:
- The replacement of one pixel value by another such that the new value is a function of only the previous value.
- polarization:
- Of an electromagnetic wave, the property that describes the orientation, i.e., time-varying direction and amplitude, of the electric field vector.
- polarized return-to-zero recording (RZR(P)):
- Return to zero recording in which the zeros are represented by signals in one sense and the ones are represented by signals in the opposite sense. (Figure 50 - Polarized return-to-zero recording).
- Polish notation:
- Synonym for prefix notation.
- polling:
- The process whereby data stations are invited one at a time to transmit. While generally used on a multipoint connection, polling can be used on a point-to-point connection. Contrast with selecting.
- polygon fill:
- The propagation of a fill pattern throughout a closed, polygonal area of a program-defined surface.
- polymorphism:
- The ability of different objects to respond to the samemessage differently.
- POP:
- point of presence.
- pop:
- To remove an item from the top of a stack. Contrast with push.
- pop-up window:
- A window that appears rapidly on the display surface in response to some action.
- port:
- (1) To make the programming changes necessary to allow a program that runs on one type of computer to run on another type of computer. (2) A termination point through which signals can enter or leave a network. (3) In a network, a functional unit through which data
can enter or leave a network. (4) A physical or logical access point for data to enter or exit; for example: a physical point of connection into a computer or data network, a logical access point at a host computer in an intranet. Synonymous with input/output port.
- portability:
- The capability of a program to be executed on various types of data processing systems with little or no modification and without converting the program to a different language.
- portable computer:
- A microcomputer that can be hand-carried for use in more than one location.
- portal:
- A starting location on a network that provides access to predefined operations.
- portrait:
- The arrangement of text or graphics on a page so that the page is oriented for normal reading when its length exceeds its width. Synonymous with portrait format, vertical format. (Figure 37 - Landscape and portrait modes)
- portrait format:
- Synonym for portrait.
- pose:
- The position and orientation of an object determined by the relationship to reference marks. A pose is characterized in terms of six degrees of freedom to specify position and orientation.
- position:
- The location of an element in a string.
- positional notation:
- A numeration system in which a number is represented by an ordered set of digits in such a way that the value contributed by a digit depends upon its position as well as upon its value. Synonymous with positional numeration system.
- positional numeration system:
- Synonym for positional notation.
- positional parameter association:
- In a subprogram call, the correspondence of an actual parameter with a formal parameter in the same position in the declaration of the subprogram. Contrast with named parameter association.
- positional representation:
- A representation of a number in a positional notation.
- positioning time:
- The sum of seek time plus search time. (Figure 1 - Access time).
- positive example:
- An example that fits the concept to be learned, and may produce a generalization of that concept. Synonymous with positive instance.
- positive instance:
- Synonym for positive example.
- post:
- In a computer conference, to make a message available to all subscribers.
- postamble:
- A sequence of bits recorded at the end of each block of data for the purpose of synchronization.
- postamble breakpoint:
- A breakpoint that is placed at an exit point from a program or subprogram.
- postcondition:
- An assertion that pertains to a point immediately following, in the execution sequence, a specified portion of a program.
- post-development review:
- Synonym for system follow-up.
- postfix notation:
- A method of forming mathematical expressions in which each operator is preceded by its operands and indicates the operation to be performed on the operands or the intermediate results that precede it. Synonymous with reverse Polish notation, suffix notation. Contrast with infix notation, prefix notation.
- post-implementation review:
- Synonym for system follow-up.
- posting:
- In a computer conference, a message available to all subscribers. Synonymous with article.
- postmortem dump:
- A dump that is produced upon abnormal termination of the execution of a program.
- postprocessor:
- A program that effects some final computation or organization.
- posttest loop:
- A loop control that performs the test after the loop body; for example, in Pascal the "repeat . . . until" construct.
- potential recipient:
- Any user or distribution list to which a message or probe may be conveyed.
- potentiometer set mode:
- That set-up mode of an analog computer during which the coefficients of the problem are set.
- power typing:
- In text processing, high-speed entry of text that is to be corrected and printed later.
- PPCS:
- production planning control system.
- PPP:
- Point-to-Point Protocol.
- pragma:
- In Ada, the term for compiler directive.
- pragmatics:
- The relationships of symbols or groups of symbols and their impact on the recipient. Contrast with semantics.
- preamble:
- (1) A specified bit pattern transmitted by a data station, that precedes a frame in order to establish synchronization with other stations. In some protocols, the preamble is part of the frame. (Figure 27 - Frame in data communication).
(2) A sequence of bits recorded at the beginning of each block of data for the purpose of synchronization.
- preamble breakpoint:
- A breakpoint that is placed at an entry point to a program or subprogram.
- precision:
- A measure of the ability to distinguish between nearly equal values; for example, four-place numerals are less precise than six-place numerals, nevertheless a properly computed four-place numeral may be more accurate than an improperly computed six-place numeral. A three-digit decimal numeral discriminates among 1000 possibilities.
- precondition:
- An assertion that pertains to a point immediately preceding, in the execution sequence, a specified portion of a program.
- predefined:
- Pertaining to a language construct that is declared by the definition of the programming language; for example, the predefined function SIN in PL/I, the predefined data type INTEGER in Fortran. Synonymous with built-in, intrinsic.
- predefined identifier:
- An identifier that is defined as part of a programming language; for example: a reserved word. If a predefined identifier is not reserved, then a declaration using that identifier redefines its meaning for the scope of the declaration.
- predefined process:
- In a flowchart, a process that is identified only by name and that is defined elsewhere.
- predefined type:
- A data type, referenced by a predefined identifier, for which a programming language provides appropriate operations.
- predicate:
- A linguistic construct in a conceptual schema language, analogous to a verb, that qualifies entities referred to in a sentence.
- prediction coding:
- In speech recognition and speech synthesis, speech coding used to encode the difference between the input signal and a predicted signal over a time window of fixed duration.
- preemptive multitasking:
- An operating mode in which the execution of programs is periodically interrupted by the operating system and control is passed to another program that has been waiting.
- prefix notation:
- A method of forming mathematical expressions in which each operator precedes its operands and indicates the operation to be performed on the operands or the intermediate results that follow it; for example, A added to B and the sum multiplied by C is represented by the expression *+ABC. Another example is, P AND the result of Q AND R is represented by the expression &P&QR. Synonymous with Lukasiewicz notation, Polish notation. Contrast with infix notation, postfix notation.
- preprocessing:
- Processing performed prior to a major process. For example: translation of a statement, written in the embedded database language SQL, into a host language.
- preprocessor:
- A program or subprogram that carries out some processing steps prior to a major process.
- preread head:
- A read head adjacent to another read head and used to read data before the same data are read by the other read head.
- prerecorded data medium:
- A data medium on which certain preliminary items of data are present, the remaining items being entered during subsequent operations. Synonymous with prerecorded medium.
- prerecorded medium:
- Synonym for prerecorded data medium.
- presentation layer:
- In OSI, the layer that provides for the selection of a common syntax for representing data and for transformation of application data into and from this common syntax. (Figure 47 - The Open Systems Interconnection Reference Model).
- presentation medium:
- A medium for the reproduction of data to a user; for example: sound as emitted by a loudspeaker; graphics as presented on a screen.
- preset:
- To establish an initial condition, such as the control values of a loop, or the value to which a parameter is to be bound.
- preset parameter:
- A parameter that is bound when a program is constructed, coded, or compiled.
- prestore:
- To store data that are required by a program before the program is entered.
- presumptive instruction:
- An instruction that does not become effective until it has been modified in a prescribed manner.
- pretest loop:
- A loop control that performs a test before entry into the loop body. Usually, a pretest loop is preferred, because a posttest loop permits one execution of the loop before the test is first performed; for example, a "for" loop in Ada.
- prevarication:
- Synonym for irrelevance.
- preventive maintenance:
- Maintenance performed according to prescribed criteria in order to reduce the probability of failure or the degradation of a functional unit.
- preview:
- In hypermedia and multimedia, a short dynamic representation of the content of a medium.
- primary cache:
- Synonym for level-one cache.
- primary index:
- An index for primary keys.
- primary key:
- A key that unambiguously identifies one record.
- primary recipient:
- A recipient for whom a message is principally intended.
- primary station:
- In high-level data link control, the part of the data station that supports the primary control functions of the data link, generates commands to be transmitted, and interprets received responses. Specific responsibilities assigned to the primary station include initialization of control signal interchange, organization of data flow, and actions regarding error control and error recovery functions.
- primary storage:
- Loosely, synonym for main storage.
- primitive:
- In OSI, an abstract description of an element of the interaction between a service user and a service provider. The OSI primitives are request, indication, response, confirm. (Figure 51 - Primitive).
- primitive instancing:
- Solid modeling that defines a set of primitive three-dimensional solid shapes that are relevant to an application area; for example, a gear may be parameterized by its diameter or number of teeth. Contrast with cell decomposition. (Figure 52 - Primitive instancing).
- principal plane:
- The imaginary plane in or near a lens where the light rays appear to bend.
- print:
- To create a permanent image of data on a removable physical medium.
- print contrast ratio:
- In optical character recognition, the ratio obtained by subtracting the reflectance at an inspection area from the maximum reflectance found within a specified distance from that area, and dividing the result by that maximum reflectance.
- print contrast signal (PCS):
- In optical character recognition, a measure of the contrast between a printed character and the paper on which the character is printed.
- print control character:
- A control character for print operations such as line spacing, page ejection, or carriage return.
- print drum:
- A rotating cylinder that presents characters at each of the possible print positions.
- printer:
- An output unit that produces a permanent image of data on a removable physical medium.
- printing calculator:
- A calculator in which the data output is printed on paper.
- print preview:
- The display of an entire page or a portion of a page of a document, closely reproducing the appearance the page will have when it is printed. The print preview function must be requested by the user, whereas a WYSIWYG display provides a continual display of pages as they will appear when printed.
- print server:
- A server that manages printing resources and is organized to facilitate use of these resources.
- print through:
- An undesired transfer of a recorded signal from one part of a magnetic medium to another part when these parts are brought into proximity.
- print to a file:
- To create a version of a document properly formatted for a particular type of printer but sent to a file instead.
- print wheel:
- A rotating disk that presents all the characters of the set at a single print position A daisywheel is a type of print wheel.
- priority interrupt:
- Suspension of the execution of a program to permit execution of another program or part of a program of higher priority.
- priority processing:
- A method of operating a computer so that the programs are executed in such a way that the order of processing is fully determined by a system of priorities.