Portable Object Adapter


Prisoner of Bill


Point Of Contact


PETRA Operator's CommAnd Language.

pocket calculator


A small battery-powered digital electronic device for performing simple arithmetic operations on data input on a keypad and outputting the result (usually a single number) to a simple LCD or other display.

The most sophisticated programmable calculators are really pocket computers which are limited to handling numerical data only.

Last updated: 1996-12-23

pocket computer



Not to be confused with P.O.D..


1. (Allegedly from abbreviation POD for "Prince Of Darkness") A Diablo 630 (or, latterly, any letter-quality impact printer). From the DEC-10 PODTYPE program used to feed formatted text to it.


2. Plain Old Documentation.

[Jargon File]

Last updated: 1998-12-18



Piece Of Data (as opposed to code).

[Jargon File]

Last updated: 2000-04-08



Any series of audio files that can be downloaded from the Internet, often released on some regular schedule, e.g. daily or weekly.

Podcasts are named after Apple Computer, Inc.'s iPod portable audio players, though most podcasts are in MP3 format and so can be played on virtually any modern audio player.

Last updated: 2009-12-16


PowerOpen Environment


A subset of Fortran.

[Mentioned in Machine Oriented Higher Level Languages, W. van der Poel, N-H 1974, p. 273].

["POFAC Description", R. Haentjens, Report 19, Cenre d'Information, Ecole Royale Militaire, Brussels, 1973].

Last updated: 1994-10-20


Probability of Failure on Demand


Early system on G-15. Listed in CACM 2(5):16 (May 1959).


<unit, text>

1. (Sometimes abbreviated "pt") The unit of length used in typography to specify text character height, rule width, and other small measurements.

There are six slightly different definitions: Truchet point, Didot point, ATA point, TeX point, Postscript point, and IN point.

In Europe, the most commonly used is Didot and in the US, the formerly standard ATA point has essentially been replaced by the PostScript point due to the demise of traditional typesetting systems and rise of desktop computer based systems running software such as QuarkXPress, Adobe InDesign and Adobe Pagemaker.

There are 20 twips in a point and 12 points in a pica (known as a "Cicero" in the Didot system).

Different point systems.

Last updated: 2004-12-23


2. To move a pointing device so that the on-screen pointer is positioned over a certain object on the screen such as a button in a graphical user interface. In most window systems it is then necessary to click a (physical) button on the pointing device to activate or select the object. In some systems, just pointing to an object is known as "mouse-over" event which may cause some help text (called a "tool tip" in Windows) to be displayed.

Last updated: 2001-05-21

point-and-drool interface


(Or "point-and-grunt interface") A parody of "point-and-shoot interface", describing a windows, icons, and mouse-based (WIMP) graphical user interface. The implication, of course, is that such an interface is only suitable for idiots.

See for the rest of us, WIMP, drool-proof paper.

[Jargon File]

Last updated: 2000-08-08

point-and-grunt interface

point-and-drool interface

pointed domain


In most formulations of domain theory, a domain is defined to have a bottom element and algebraic CPOs without bottoms are called "predomains". David Schmidt's domains do not have this requirement and he calls a domain with a bottom "pointed".

Last updated: 1999-07-07



1. An address, from the point of view of a programming language. A pointer may be typed, with its type indicating the type of data to which it points.

The terms "pointer" and "reference" are generally interchangeable although particular programming languages often differentiate these two in subtle ways. For example, Perl always calls them references, never pointers. Conversely, in C, "pointer" is used, although "a reference" is often used to denote the concept that a pointer implements.

Anthony Hoare once said:

Pointers are like jumps, leading wildly from one part of the data structure to another. Their introduction into high-level languages has been a step backward from which we may never recover.

[C.A.R.Hoare "Hints on Programming Language Design", 1973, Prentice-Hall collection of essays and papers by Tony Hoare].

<operating system>

2. (Or "mouse pointer") An icon, usually a small arrow, that moves on the screen in response to movement of a pointing device, typically a mouse. The pointer shows the user which object on the screen will be selected etc. when a mouse button is clicked.

Last updated: 1999-07-07

pointer swizzling


pointing device


Any hardware component that allows a user to input spatial data to a computer. CAD systems and Graphical User Interfaces (GUI) allow the user to control and provide data to the computer using physical "gestures" - point, click, and drag - typically by moving a hand-held mouse across the surface of the physical desktop and activating switches on the mouse. Movements of the pointing device are echoed on a graphical representation of a desktop on the screen by movements of the mouse pointer and other visual changes.

While the most common pointing device by far is a mouse, other kinds include tracker ball, trackpad, lightpen, various kinds of digitising tablets which use a stylus, and even a special "data glove" that translates the user's movements to computer gestures.

Last updated: 1997-02-03

pointing stick


Point Of Contact


(POC) An individual associated with a particular Internet entity (IP network, domain, ASN).

Last updated: 1998-09-07

point of presence

(PoP) A site where there exists a collection of telecommunications equipment, usually modems, digital leased lines and multi-protocol routers. An Internet access provider may operate several PoPs distributed throughout their area of operation to increase the chance that their subscribers will be able to reach one with a local telephone call. The alternative is for them to use virtual PoPs (virtual points of presence) via some third party.

Last updated: 1994-12-13

point of sale terminal


(Or "POS") A computer, probably with a bar code reader, serving as a glorified cash register.

Last updated: 1997-11-23

Point-to-Point Protocol

<communications, protocol>

(PPP) The protocol defined in RFC 1661, the Internet standard for transmitting network layer datagrams (e.g. IP packets) over serial point-to-point links.

PPP has a number of advantages over SLIP; it is designed to operate both over asynchronous connections and bit-oriented synchronous systems, it can configure connections to a remote network dynamically, and test that the link is usable. PPP can be configured to encapsulate different network layer protocols (such as IP, IPX, or AppleTalk) by using the appropriate Network Control Protocol (NCP).

RFC 1220 describes how PPP can be used with remote bridging.

Usenet newsgroup: comp.protocols.ppp.

A paper on PPP.

Last updated: 1994-12-13

Point-to-Point Protocol over ATM


(PPPoA) A network protocol for encapsulating PPP frames in ATM AAL5. It is used mainly with cable modem, DSL and ADSL services.

PPPoA offers standard PPP features such as authentication, encryption, and compression. It is very slightly more efficient than PPPoE and, like PPPoE, supports VC-MUX and LLC encapsulation.

PPPoA is specified in RFC 2364.

Last updated: 2007-06-15

Point-to-Point Protocol over Ethernet

<communications, protocol>

(PPPoE) The protocol defined in RFC 2516 that allows one or more computers to connect to the Internet via a shared modem. The computers connect to the modem via a local area network such as Ethernet and the modem connects to an Internet Service Provider (ISP) via a serial connection such as PPP over ADSL.

PPPoE provides each user with a connection that looks and behaves like a point-to-point dial-up connection even though they are actually sharing an Ethernet or wireless network. At the same time, the ISP only needs to provide a single Internet connection, with the same kind of accounting as for PPP. Also, the IP address is only assigned when the PPPoE connection is open, allowing the dynamic reuse of IP addresses via DHCP.

PPPoE works by encapsulating PPP frames in Ethernet frames.

Last updated: 2006-09-20

Point-to-Point Tunneling Protocol

<communications, protocol>

(PPTP) A tunneling protocol for connecting Windows NT clients and servers over Remote Access Services (RAS). PPTP can be used to create a Virtual Private Network between computers running NT. It is an extension of PPP sponsored by Microsoft.

Microsoft Point to Point Encryption may be used with PPTP to provide an encrypted connection but PPTP itself does not use encryption.

Compare: Layer Two Tunneling Protocol.

[Origin? Standard? Document?]

Last updated: 1998-09-23

Poisson distribution


A probability distribution used to describe the occurrence of unlikely events in a large number of independent trials.

Poisson distributions are often used in building simulated user loads.


Last updated: 2003-03-18


Plain Old Java Object

[As opposed to?]


The BASIC command to write a value to an absolute address.

See peek.

[Jargon File]

Last updated: 1995-01-31

Pokémon exception handling

<programming, humour>

A humourous term for a try-catch exception handling construct with no constraint on which exceptions will be caught, for when you just "Gotta Catch 'Em All." (a slogan used in the Pokémon media empire).

Pokémon is a trademark of the Pokémon Company of Japan.

[Dodgy Coder].

Last updated: 2012-07-10



An object-oriented parallel logic programming language, built on top of Parlog.

["Polka: A Parlog Object-Oriented Language", Andrew Davison, TR, Parlog Group, Imperial College, London 1988].

Last updated: 1995-01-31


To check the status of an input line, sensor, or memory location to see if a particular external event has been registered.

Contrast interrupt.

[Jargon File]

Last updated: 1995-01-31





1. A polymorphic, block-structured language developed by D.C.J. Matthews at Cambridge in the early 1980s.

["An Overview of the Poly Programming Language", D.C.J. Matthews, in Data Types and Persistence, M.P. Atkinson et al eds, Springer 1988].

2. A language developed at St Andrews University, Scotland.

[Software Practice & Exp, Oct 1986].

3. A polymorphic language used in the referenced book.

["Polymorphic Programming Languages", David M. Harland, Ellis Horwood 1984].

Last updated: 2000-11-07

polygon pusher

(Or "rectangle slinger"). A chip designer who spends most of his or her time at the physical layout level (which requires drawing *lots* of multi-coloured polygons).

[Jargon File]



A distributed language integrating classes with a parallel block structure, including multiprocedures and fragments.

["Operational Semantics of a Distributed Object-Oriented Language and its Z Formal Specification", M. Benveniste <[email protected]>, TR532, IRISA/INRIA-Rennes].

Last updated: 1995-10-17



A property of a data-object that can exist in many shapes and sizes, but not simultaneously; which distinguishes it from a union. It is often implemented as a set of classes (or structs) derived from a common base class (or with a common header, as in the case of structs), typically without any methods.

It has been loosely described as polymorphic data.


Last updated: 1996-01-07



SML implemented in D.C.J. Matthews's Poly, for Motorola 68020 and SPARC by Abstract Hardware Ltd.

Last updated: 1999-11-23



polymorphic lambda-calculus

<language, types>

(Or "second order typed lambda-calculus", "System F", "Lambda-2"). An extension of typed lambda-calculus allowing functions which take types as parameters. E.g. the polymorphic function "twice" may be written:

 	twice = /\ t . \  (f :: t -> t) . \ (x :: t) . f (f x)

(where "/\" is an upper case Greek lambda and "(v :: T)" is usually written as v with subscript T). The parameter t will be bound to the type to which twice is applied, e.g.:

 twice Int

takes and returns a function of type Int -> Int. (Actual type arguments are often written in square brackets [ ]). Function twice itself has a higher type:

 twice :: Delta t . (t -> t) -> (t -> t)

(where Delta is an upper case Greek delta). Thus /\ introduces an object which is a function of a type and Delta introduces a type which is a function of a type.

Polymorphic lambda-calculus was invented by Jean-Yves Girard in 1971 and independently by John C. Reynolds in 1974.

["Proofs and Types", J-Y. Girard, Cambridge U Press 1989].

Last updated: 2005-03-07


<theory, programming>

The ability to leave parts of a type in a typed language unspecified. The term has three distinct uses:

* Parametric polymorphism refers to the use of type variables in a strongly typed language.

* Overloading, sometimes called ad-hoc polymorphism, means using the same syntax for different types.

* object-oriented polymorphism allows a variable to refer to objects whose class is not known at compile time.

Last updated: 2014-01-05



1. An arithmetic expression composed by summing multiples of powers of some variable.

 P(x) = sum a_i x^i for i = 0 .. N

The multipliers, a_i, are known as "coefficients" and N, the highest power of x with a non-zero coefficient, is known as the "degree" of the polynomial. If N=0 then P(x) is constant, if N=1, P(x) is linear in x. N=2 gives a "quadratic" and N=3, a "cubic".


2. polynomial-time.



(P) The set or property of problems which can be solved by a known polynomial-time algorithm.

Last updated: 1995-04-10

polynomial-time algorithm


A known algorithm (or Turing Machine) that is guaranteed to terminate within a number of steps which is a polynomial function of the size of the problem.

See also computational complexity, exponential time, nondeterministic polynomial-time (NP), NP-complete.

Last updated: 1995-04-13

polyvinyl chloride


(PVC) A common plastic used for insulating and jacketing many wire and cable products.

Last updated: 2001-03-26


phase of the moon

Usually used in the phrase "POM-dependent", which means flaky.

Last updated: 1995-04-10



Algorithmic art by Denis Howe.

View pompom.

Last updated: 2018-01-01


A non-strict polymorphic, functional language by Jon Fairbairn <[email protected]>.

Ponder's type system is unusual. It is more powerful than the Hindley-Milner type system used by ML and Miranda and extended by Haskell. Ponder adds extra recursive 'mu' types to those of Girard's System F, allowing more general recursion. Surprisingly, the type system and type inference algorithm are still not completely understood.

["Ponder and its Type System", J. Fairbairn, TR 31, Cambridge U Computer Lab, Nov 1982].

[J. Fairbairn, "Design and Implementation of a Simple Typed Language based on the Lambda-Calculus", Technical Report No. 75, Computer Laboratory, University of Cambridge, May 1985].

[J. Fairbairn, "A New Type-Checker for a Functional Language", Technical Report No. 53, Computer Laboratory, University of Cambridge, 1984].

[J. Fairbairn, "Some Types with Inclusion Properties in \forall, \rightarrow, \mu", Technical Report No. 171, Computer Laboratory, University of Cambridge, Jun 1989].

[Valeria C. V. de Paiva, "Subtyping in Ponder (Preliminary Report)", Technical Report No. 203, Computer Laboratory, University of Cambridge, Aug 1990].



A computer game invented in 1972 by Atari's Nolan Bushnell. The game is a minimalist rendering of table tennis. Each of the two players are represented as a white slab, controllable by a knob, which deflects a bouncing ball. The goal of the game is to "AVOID MISSING BALL FOR HIGH SCORE".


Last updated: 1997-11-23


Parallel Object-Oriented Language.

A series of languages from Philips Research Labs.


Last updated: 1995-02-07


Parallel Object-Oriented Language 2.

Philips Research Labs, 1987.

Strongly typed, synchronous message passing, designed to run on DOOM (DOOM = Decentralised Object-Oriented Machine).

["POOL and DOOM: The Object- Oriented Approach", J.K. Annot, PAM den Haan, in Parallel Computers, Object-Oriented, Functional and Logic, P. Treleaven ed].

["Issues in the Design of a Parallel Object-Oriented Language", P. America, Formal Aspects of Computing 1(4):366-411 (1989)].

Last updated: 1995-02-07


One of the POOL languages.

["A Parallel Object-Oriented Language with Inheritance and Subtyping", P. America et al, SIGPLAN Notices 25(10):161-168 (OOPSLA/ECOOP '90) (Oct 1990)].

Last updated: 1995-02-07

Pooling Agreement for Technical Assistance


(PATA) Written limitations on what types of technical information is shared when two companies (or departments) work together on a common project. Often because of security concerns rather than marketing concerns.

Last updated: 2010-02-20


Object-oriented, concurrent, synchronous. Predecessor of POOL2.

["Definition of the Programming Language POOL-T", Esprit Project 415, Doc. 0091, Philips Research Labs, Eindhoven, Netherlands, June 1985].

Last updated: 1995-02-07



1. A family of programming languages, POP-1, POP-2, POP-10, Pop-11, POP++, POP-9X, POPLOG.

2. Post Office Protocol.

See also pop, PoP.

[Jargon File]

Last updated: 1996-02-18


Point Of Presence



To remove something from the top of a stack.

Opposite of push.

(Not to be confused with Post Office Protocol or POP-1 the language).

[Jargon File]

Last updated: 1996-02-18


An object-oriented extension of POPLOG. Available from Integral Solutions.

[Jargon File]


Package for Online Programming. Edinburgh, 1966. First of the POP family of languages. Used reverse Polish notation. Implemented as a threaded interpreter. EPU-R-17, U Edinburgh (Jul 1966). "POP-1: An Online Language", R. Popplestone, Mach Intell 2, E. Dale et al eds, Oliver and Boyd, Edinburgh 1968.


Descendant of POP-2, for the PDP-10 by Julian Davies, 1973. ["POP-10 User's Manual", D.J.M. Davies, CS R25, U West Ontario, 1976].



A programming language created by Robin Popplestone in 1975, originally for the PDP-11. Pop-11 is stack-oriented, extensible, and efficient like FORTH. It is also functional, dynamically typed, interactive, with garbage collection like LISP, and the syntax is block structured like Pascal.

["Programming in POP-11", J. Laventhol <[email protected]>, Blackwell 1987].

AlphaPop is an implementation for the Macintosh from Computable Functions Inc. PopTalk and POPLOG from the University of Sussex are available for VAX/VMS and most workstations.

E-mail: Robin Popplestone <[email protected]>

Last updated: 2003-03-25


Robin POPplestone, Edinburgh, 1967. An innovative language incorporating many of Landin's ideas, including streams, closures, and functions as first-class citizens. ALGOL-like syntax. The first implementation was named Multi-POP, based on a REVPOL function written in POP-1, producing the reverse-polish form as output. "POP-2 Papers", R.M. Burstall et al, Oliver & Boyd 1968. "Programming in POP-2", R.M. Burstall et al, Edinburgh U Press 1971. "POP-2 User's Manual", R. Popplestone, Mach Intell 2, E. Dale et al eds, Oliver and Boyd, Edinburgh 1968.


<messaging, protocol>

Version 3 of the Post Office Protocol. POP3 is defined in RFC 1081, written in November 1988 by Marshall Rose, which is based on RFC 918 (since revised as RFC 937). POP3 allows a client computer to retrieve electronic mail from a POP3 server via a (temporary) TCP/IP or other[?] connection. It does not provide for sending mail, which is assumed to be done via SMTP or some other method.

POP is useful for computers, e.g. mobile or home computers, without a permanent network connection which therefore require a "post office" (the POP server) to hold their mail until they can retrieve it.

Although similar in form to the original POP proposed for the Internet community, POP3 is similar in spirit to the ideas investigated by the MZnet project at the University of California, Irvine, and is incompatible with earlier versions of POP.

Substantial work was done on examining POP in a PC-based environment. This work, which resulted in additional functionality in this protocol, was performed by the ACIS Networking Systems Group at Stanford University.

RFC 1082 (POP3 Extended Service) extends POP3 to deal with accessing mailboxes for mailing lists.

Last updated: 1997-01-09


Proposed BSI standard for Pop-11.


A grammar-driven programming environment generator. Uses Paddle.

["POPART: Producer of Paddles and Related Tools, System Builders' Manual", D.S. Wile TR RR-82-21, ISI, Marina del Rey, CA 1982].

Last updated: 1994-11-30


AI system built on POP-2. "The POPCORN Reference Manual", S. Hardy, Essex U, Colchester, 1973.

pop-down menu

pull-down menu


/pop'J/ [PDP-10 return-from-subroutine instruction]. To return from a digression. By verb doubling, "Popj, popj" means roughly "Now let's see, where were we?" See RTI.

[Jargon File]


Morris, 1978. A blend of LISP with SNOBOL4 pattern matching and APL-like postfix syntax. Implicit iteration over lists, sorting primitive. "Experience with an Applicative String-Processing Language", J.H. Morris et al, 7th POPL, ACM 1980, pp.32-46.


A PLANNER-type language for the POP-2 environment.

["Popler 1.6 Reference Manual", D. Davies et al, U Edinburgh, TPU Report No 1 (May 1973)].


A multi-language programming environment, which includes the languages Pop-11, ML, Common Lisp and Prolog. It supports mixed-language programming and incremental compilation and includes a comprehensive X Window System interface. It is built on top of a two-stack virtual machine, PVM. POPLOG was developed at the University of Sussex, Brighton, UK.

["POPLOG's Two-Level Virtual Machine Support for Interactive Languages", R. Smith et al, in Research Directions in Cognitive Science, v.5 (1992)].


SML for the Poplog system from the University of Sussex, UK.

POP server

Post Office Protocol


<language, product>

A commercial object-oriented derivative of POP, from Cambridge Consultants, used in the expert system MUSE.

Last updated: 1995-02-27

PopularitY of Programming Languages


(PYPL) An index like Tiobe showing the popularity of programming languages based by analyzing searches for language tutorials on Google.


Last updated: 2020-01-31


power-on reset







Still and moving images, usually of women, in varying states of nudity, posing or performing erotic acts with men, women, animals, machines, or other props. Some say it degrades women, some say it corrupts young boys (who down-load it from the web or exchange it on floppy disks). Most of it is in the form of JPEG images. Many websites offer porn of all sorts, almost always for a subscription. It is said that these are a driving force in the evolution of new technology and techniques for the web. Advertisments for them certainly constitute a significant proportion of all spam. There are even pornographic computer games, an early example being Mac Playmate.

Beware - many institutions, particularly universities, have strict rules against their computers and networks being used to transfer or store such things, and you might get corrupted.

Last updated: 2002-03-08



1. A logical channel or channel endpoint in a communications system. The Transmission Control Protocol and User Datagram Protocol transport layer protocols used on Ethernet use port numbers to distinguish between (demultiplex) different logical channels on the same network interface on a computer.

Each application program has a unique port number associated with it, defined in /etc/services or the Network Information Service "services" database. Some protocols, e.g. telnet and HTTP (which is actually a special form of telnet) have default ports specified as above but can use other ports as well.

Some port numbers are defined in RFC 3232 (which replaces RFC 1700). Ports are now divided into: "Well Known" or "Privileged", and "Ephemeral" or "Unprivileged" (comprising "Registered", "Dynamic", "Private").

Last updated: 2004-12-30

<operating system, programming>

2. To translate or modify software to run on a different platform, or the results of doing so. The portability of the software determines how easy it is to port.


3. An imperative language descended from Zed from Waterloo Microsystems (now Hayes Canada) ca. 1979.

["Port Language" document in the Waterloo Port Development System].

Last updated: 2002-06-19


<operating system, programming>

The ease with which a piece of software (or file format) can be "ported", i.e. made to run on a new platform and/or compile with a new compiler.

The most important factor is the language in which the software is written and the most portable language is almost certainly C (though see Vaxocentrism for counterexamples). This is true in the sense that C compilers are available for most systems and are often the first compiler provided for a new system. This has led several compiler writers to compile other languages to C code in order to benefit from its portability (as well as the quality of compilers available for it).

The least portable type of language is obviously assembly code since it is specific to one particular (family of) processor(s). It may be possible to translate mechanically from one assembly code (or even machine code) into another but this is not really portability. At the other end of the scale would come interpreted or semi-compiled languages such as LISP or Java which rely on the availability of a portable interpreter or virtual machine written in a lower level language (often C for the reasons outlined above).

The act or result of porting a program is called a "port". E.g. "I've nearly finished the Pentium port of my big bang simulation."

Portability is also an attribute of file formats and depends on their adherence to standards (e.g. ISO 8859) or the availability of the relevant "viewing" software for different platforms (e.g. PDF).

Last updated: 1997-06-18



Portable AIRTIME

<communications, wireless>

A wireless, digital communications system enabling user-to-user voice communication, "quicknotes", and alphanumeric messaging.


Last updated: 2000-12-07

Portable Commodore 64


A version of the Commodore 64 modelled after the original Osborne portable PCs, with a flip-down keyboard that revealed a 5-inch colour monitor, and a built-in 1541 floppy disk drive. It is thought that few were made but that they did go on sale, at least in Canada.

[Relationship to Commodore 65?]

Last updated: 1997-09-14

Portable Common Loops

(PCL) A language which started out as an implementation of CommonLoops and turned into a portable CLOS implementation. Version 1992-08-28. It runs under Lucid Common LISP 4.0.1 and CMU Common LISP 16e.


Last updated: 1992-09-02

[Was it developed by Richard Harris <[email protected]>?]

Portable Common Tool Environment


(PCTE) An ECMA standard framework for software tools developed in the Esprit programme. It is based on an entity-relationship Object Management System and defines the way in which tools access this.

Last updated: 2001-03-03

portable computer


(Commonly, "laptop") A portable personal computer you can carry with one hand. Some laptops run so hot that it would be quite uncomforable to actually use them on your lap for long. The term "notebook" is often used to describe these, though it also implies a low weight (less than 2kg). A "luggable" is one you could carry in one hand but is so heavy you wouldn't want to. One that can by easily operated while held in one hand is a "palmtop".

The computer considered by most historians to be the first true portable computer was the Osborne 1 but see the link below for other contenders.

History of laptop computers.

Last updated: 2007-05-21

Portable Document Format

<file format>

(PDF) The native file format for Adobe Systems' Acrobat. PDF is the file format for representing documents in a manner that is independent of the original application software, hardware, and operating system used to create those documents. A PDF file can describe documents containing any combination of text, graphics, and images in a device-independent and resolution independent format. These documents can be one page or thousands of pages, very simple or extremely complex with a rich use of fonts, graphics, colour, and images.


["The Portable Document Format Reference Manual", Adobe systems, Inc. Addison-Wesley Publ. Co., ISBN: 0-201-62628-4].

Last updated: 2000-09-08

Portable Forth Environment


(PFE) A highly portable Forth development system based on the ANSI standard for Forth, by Dirk-Uwe Zoller of FHT, Mannheim, Germany. PFE aims to be correct, complete, usable, and simple but it isn't optimised for speed. It supports all dpANS word sets. It runs on Linux, RS/6000, and HP-UX.

Tektronix adopted PFE in 1998 and added modules and multithreading. You can load additional C objects at run time to extend the Forth dictionary. It can be targeted at different embedded environments by changing the terminal driver and initilisation routines.


E-mail: Guido Draheim <[email protected]>.

Last updated: 2000-12-07

Portable Network Graphics

<file format>

/ping/ (PNG) An extensible file format for the lossless, portable, well-compressed storage of raster images. PNG provides a patent-free replacement for GIF and can also replace many common uses of TIFF. Indexed-colour, greyscale and truecolour images are supported, plus an optional alpha channel. Sample depths range from 1 to 16 bits.

PNG is designed for on-line viewing applications, such as the World Wide Web, so it is fully streamable with a progressive display option. PNG is robust, providing both full file integrity checking and simple detection of common transmission errors. Also, PNG can store gamma correction and chromaticity data for improved colour matching on heterogeneous platforms.

Filename extension: .png.

RFC 2083. W3C PNG pages. PNG home page.

Last updated: 1997-08-07

Portable Object Adapter


(POA) Part of the CORBA architecture.


Last updated: 2004-06-23

Portable Operating System Interface

<operating system, standard>

(POSIX) A set of IEEE standards designed to provide application portability between Unix variants. IEEE 1003.1 defines a Unix-like operating system interface, IEEE 1003.2 defines the shell and utilities and IEEE 1003.4 defines real-time extensions.

["More UNIX For Dummies", ISBN: 1-56884-361-5] says it stands for "Portable Operating System Interface with an X thrown in to make it sound cooler."

Last updated: 1997-12-04

Portable Pixmap

<file format>

(PPM) A colour image file format.

A PPM file contains the following:

 a two character "{magic number}" - "P3",
 the width in pixels,
 the height in pixels,
 the maximum colour component value,
 HEIGHT rows of WIDTH {pixels}.

The rows are ordered from top to bottom with the pixels in each row ordered from left to right. Each pixel is represented as three values for red, green, and blue.

All parts are separated by whitespace and numbers are in decimal ASCIII representation. A zero pixel component means that colour is absent. Characters from a "#" to the next end-of-line are ignored and no line should be longer than 70 characters.

Here is an example of a small pixmap in this format:

 # feep.ppm
 4 4
  0  0  0    0  0  0    0  0  0   15  0 15
  0  0  0    0 15  7    0  0  0    0  0  0
  0  0  0    0  0  0    0 15  7    0  0  0
 15  0 15    0  0  0    0  0  0    0  0  0

A "RAWBITS" variant has magic number "P6", pixel values are stored as plain binary bytes, instead of ASCII decimal and no whitespace is allowed after a single whitespace character after the maximum colour component value which must be less than or equal to 255.

Last updated: 1998-02-06

Portable Scheme Debugger

(PSD) A package for source code debugging of R4RS-compliant Scheme under GNU Emacs by Kellom ?ki Pertti <[email protected]>. Version 1.1. Distributed under GNU GPL. It works with scm, Elk and Scheme->C.


Last updated: 1992-10-08

Portable Scheme Interpreter

(PSI) A portable scheme interpreter by Ozan Yigit <[email protected]rku.ca>, David Keldsen and Pontus Hedman that includes a simple DAG compiler and a virtual machine. It can be used as an integrated extension interpreter in other systems and allows easy addition of new primitives. There are some unique debugging and tracing facilities. Acceptable performance results from a fairly straight-forward implementation. Continuations are fully and portably supported and perform well. PSI is based on the simple compilers and virtual machine in Kent Dbyvig's thesis.

The pre-release version conforms to R4RS with a number of useful extensions.

Last updated: 1993-02-19

Portable Standard Lisp


(PSL) A dialect of Lisp from Utah University. PSL is available as a kit for 68000 and also runs on VAX. It compiles Lisp to C-code virtual machine language.

["The Portable Standard LISP Users Manual", TR-10, CS Dept, U Utah, Jan 1982].

["A Portable Lisp System", M.L. Griss et al, Proc 1982 ACM Symp on Lisp and Functional Prog, Aug 1982].

Last updated: 2000-09-25

Portable Tool Interface

<programming, standard>

(PTI) A standard such as PCTE, allowing interworking between different software tools via defined interfaces to the user and to the repository or object management system.

Last updated: 2000-09-25

Port Address Translation


(PAT) A function provided by some routers which allows hosts on a LAN to communicate with the rest of a network (such as the Internet) without revealing their own private IP address. All outbound packets have their IP address translated to the routers external IP address. Replies come back to the router which then translates them back into the private IP address of the original host for final delivery.

Compare SOCKS.

Last updated: 1998-05-08


Process-Oriented Real-Time Algorithmic Language.

["PORTAL - A Pascal-based Real-Time Programming Language", R. Schild in Algorithmic Languages, J.W. deBakker et al eds, N-H 1981].



A website that aims to be an entry point to the web, typically offering a search engine and/or links to useful pages, and possibly news or other services. These services are usually provided for free in the hope that users will make the site their default home page or at least visit it often. Popular examples are Yahoo and MSN. Most portals on the Internet exist to generate advertising income for their owners, others may be focused on a specific group of users and may be part of an intranet or extranet. Some may just concentrate on one particular subject, say technology or medicine, and are known as a vertical portals.

Last updated: 2001-07-07


Translating software to run on a different computer and/or operating system.

Last updated: 1995-01-06

Port Language

["Communicating Parallel Processes", J. Kerridge et al, Soft Prac & Exp 16(1):63-86 (Jan 1986)].



A server that converts TCP/IP protocol port numbers into RPC program numbers. It must be running in order to make RPC calls.

When an RPC server starts, it tells portmap the port number it is listening on and what RPC program numbers it serves. Before a client can call a given RPC program number, it must contacts portmap on the server machine to determine the port number to which RPC packets should be sent.

Last updated: 1996-12-09

port number



point of sale


<language A query language written in 1967.

["POSE: A Language for Posing Problems to Computers", S. Schlesinger et al, CACM 10:279-285, May 1967].

Last updated: 1996-12-09


partially ordered set

positional representation


The conventional way of writing numbers as a string of digits in which each digit, D, has value D * R^I, where R is the radix or (number) base and I is the digit's position counting leftward from zero at the least significant (right-hand) end. Each digit can be zero to R-1. Each position has a weight or significance R times greater than the position to its right and the right-most place has a weight of one.

Decimal numbers are radix ten, binary numbers are radix two, octal radix eight and hexadecimal radix 16.

Positional representation makes arithmetic operations on large numbers much easier than, say, roman numerals. It is fundamental to the binary representation used by digital computers.

Last updated: 2006-11-10


Portable Operating System Interface

POSIX Threads


(Pthreads) A POSIX standard API that defines a set of C programming language types, functions and constants for creating and manipulating pre-emptive threads.

The standard's full name is "POSIX.1c, Threads extensions (IEEE Std 1003.1c-1995)". Implementations are available on many Unix-like POSIX-conformant operating systems such as FreeBSD, NetBSD, OpenBSD, GNU/Linux, Mac OS X and Solaris as well as DR-DOS and Microsoft Windows.

Pthreads was designed and implemented in the PART Project (POSIX / Ada-Runtime Project).

Last updated: 2012-04-18


power-on self-test



To send a message to a mailing list or newsgroup. Usually implies that the message is sent indiscriminately to multiple users, in contrast to "mail" which implies one or more deliberately selected individual recipients.

You should only post a message if you think it will be of interest to a significant proportion of the readers of the group or list, otherwise you should use private electronic mail instead. See netiquette.

[Jargon File]

Last updated: 1997-12-04


Shareware that borders on freeware, in that the author requests only that satisfied users send a postcard of their home town or something. (This practice, silly as it might seem, serves to remind users that they are otherwise getting something for nothing, and may also be psychologically related to real estate "sales" in which $1 changes hands just to keep the transaction from being a gift.)

[Jargon File]

posted write-through

A cache with a posted write-through policy (e.g. Intel 80386) delays the write-back to main memory until the bus is not in use.

Postel, Jon

Jon Postel

postfix notation


(Or "Reverse Polish Notation", RPN) One of the possible orderings of functions and operands: in postfix notation the functions are preceded by all their operands. For example, what may normally be written as "1+2" becomes "1 2 +". Postfix notation is well suited for stack based architectures but modern compilers reduced this advantage considerably.

The best-known language with postfix syntax is FORTH. Some Hewlett-Packard calculators use it, e.g. HP-25, HP-29C, HP-41C, HP-23SII.

Compare: infix notation, prefix notation.

Last updated: 2003-06-23

postfix syntax

postfix notation



An active DBMS developed at the University of California at Berkeley by a team led by Michael Stonebraker (1986-1994). Postgres was later taken by Illustra and developed into a commercial product, which in turn was bought by Informix and integrated into their product, Universal Server.

PostgreSQL is a further development of the original POSTGRES code as a free software alternative to commercial DBMS vendor offerings.

[Details? Reference? Relationship to Ingres?]

Last updated: 1999-07-04



/'post-gres-kyu-el/ An enhancement of the POSTGRES database system.

PostgreSQL is an advanced relational database management system with some object oriented approaches. PostgreSQL is developed and distributed as free software, and while retaining its freedom it remains technically and featurewise a worthy competitor to even the most advanced commercial alternatives.

It was also one of the first databases to offer MVCC as opposed to row-level locking or table locking, thereby greatly improving multi-user performance.

PostgreSQL implements an extended subset of ANSI SQL and runs on many platforms. It also has interfaces to many different programming languages and database protocols, like ODBC and JDBC.


Last updated: 1999-09-18


A message sent to a newsgroup or mailing list (may also be called "a post") or the act of sending it. Distinguished from a "letter" or ordinary electronic mail message by the fact that it is broadcast rather than point-to-point. It is not clear whether messages sent to a small mailing list are postings or e-mail; perhaps the best dividing line is that if you don't know the names of all the potential recipients, it is a posting.

[Jargon File]


The electronic mail contact and maintenance person at a site connected to the Internet or UUCPNET. Often, but not always, the same as the admin. The Internet standard for electronic mail (RFC 822) requires each machine to have a "postmaster" address; usually it is aliased to this person. See also webmaster.

post office problem


Given a set of points (in N dimensions), find another point which minimises the sum of the distances from that point to each of the others.

Last updated: 2007-03-07

Post Office Protocol

<messaging, protocol>

(POP) A protocol designed to allow single-user computers to retrieve electronic mail from a POP server via TCP/IP. The default port is 110.

The POP server might be a computer with a permanent Internet connection whereas its clients might only connect to it occasionally, e.g. by modem.

There are (in 1994) three versions: POP, POP2, and POP3. Later versions are NOT compatible with earlier ones.


Last updated: 2007-03-07

post-order traversal



POSTGRES QUERy Language. The language used by the POSTGRES database system.

["The Design of POSTGRES", M. Stonebraker et al, Proc ACM SIGMOD Conf, June 1986].

Version 4.0.


<language, text, graphics>

A page description language based on work originally done by John Gaffney at Evans and Sutherland in 1976, evolving through "JaM" ("John and Martin", Martin Newell) at XEROX PARC, and finally implemented in its current form by John Warnock et al. after he and Chuck Geschke founded Adobe Systems, Inc. in 1982.

PostScript is an interpreted, stack-based language (like FORTH). It was used as a page description language by the Apple LaserWriter, and now many laser printers and on-screen graphics systems. Its primary application is to describe the appearance of text, graphical shapes, and sampled images on printed or displayed pages.

A program in PostScript can communicate a document description from a composition system to a printing system in a device-independent way.

PostScript is an unusually powerful printer language because it is a full programming language, rather than a series of low-level escape sequences. (In this it parallels Emacs, which exploited a similar insight about editing tasks). It is also noteworthy for implementing on-the fly rasterisation, from Bezier curve descriptions, of high-quality fonts at low (e.g. 300 dpi) resolution (it was formerly believed that hand-tuned bitmap fonts were required for this task).

PostScript's combination of technical merits and widespread availability made it the language of choice for graphical output until PDF appeared.

The Postscript point, 1/72 inch, is slightly different from other point units.

An introduction.

["PostScript Language Reference Manual" ("The Red Book"), Adobe Systems, A-W 1985].

[Jargon File]

Last updated: 2002-03-11

Postscript point

<unit, text>

The variant of the point used by Postscript, equal to 0.3527777778 mm, or 1/72 inch.

Last updated: 2002-03-11

Post, Telephone and Telegraph administration

<communications, company>

(PTT) One of the many national bodies responsible for providing communications services in a particular country. Traditionally, PTTs had monopolies in their respective countries. This monopoly was first broken in the USA, with the UK joining somewhat later. Currently the markets are being deregulated in Europe as well as other parts of the world.

Well-known PTTs include MCI, AT&T, and British Telecom.

Compare: telco.

Last updated: 1998-05-18


Programming system for distributed applications. A Linda implementation for Unix networks by Ioannis Schoinas <[email protected]>.


Last updated: 1995-12-04

potential difference



Plain Old Telephone Service



A British pound sign or Americal hash character.

Last updated: 2013-08-15

pound on

bang on

pound sign


"£", ASCII character 163, 0xA3. A stylised capital "L" used to prefix amounts in British pounds sterling (GBP).

Americans call the hash character ("#") "pound" but that is an antiquated reference to pounds weight (lb).

Last updated: 2013-08-15


Performance Optimization with Enhanced RISC. The IBM processor architecture on which PowerPC was based.


<tool, database>

A graphical user interface development tool from Powersoft for developing client-server database applications. It runs under MS-DOS(?) and Microsoft Windows. There are also versions for Microsoft Windows, Windows NT, Macintosh, and Unix.

Applications can be built by creating windows, controls (such as listboxes and buttons), and menus within the PowerBuilder development environment. The language used to program PowerBuilder, PowerScript, is loosely based on BASIC.

PowerBuilder supports programming on many database backends including Sybase and Oracle. It also has added support for ODBC database drivers. PowerBuilder also comes with a built-in database backend (WATCOM SQL 32-bit relational database).

Product information.


Usenet newsgroup: comp.soft-sys.powerbuilder.

[Correct list of platforms?]

Last updated: 2001-03-23

power cycle


(Or "cycle power", "cycle") To turn a machine's power off and on, with the intention of clearing some kind of hung or gronked state. Synonym 120 reset; see also Big Red Switch. Compare Vulcan nerve pinch, bounce and boot, and see the AI Koan about Tom Knight and the novice.

[Jargon File]

Last updated: 2012-02-09



The powerdomain of a domain D is a domain containing some of the subsets of D. Due to the asymmetry condition in the definition of a partial order (and therefore of a domain) the powerdomain cannot contain all the subsets of D. This is because there may be different sets X and Y such that X <= Y and Y <= X which, by the asymmetry condition would have to be considered equal.

There are at least three possible orderings of the subsets of a powerdomain:


 X <= Y  iff  for all x in X, exists y in Y: x <= y
         and  for all y in Y, exists x in X: x <= y

("The other domain always contains a related element").

Hoare or Partial Correctness or Safety:

 X <= Y  iff  for all x in X, exists y in Y: x <= y

("The bigger domain always contains a bigger element").

Smyth or Total Correctness or Liveness:

 X <= Y  iff  for all y in Y, exists x in X: x <= y

("The smaller domain always contains a smaller element").

If a powerdomain represents the result of an abstract interpretation in which a bigger value is a safe approximation to a smaller value then the Hoare powerdomain is appropriate because the safe approximation Y to the powerdomain X contains a safe approximation to each point in X.

("<=" is written in LaTeX as \sqsubseteq).

Last updated: 1995-02-03



A language combining functional programming and logic programming, using "angelic Powerdomains".

Last updated: 1998-06-30

power hit

(Or "power glitch") A sudden increase (spike) or decrease (drop-out) in the mains electricity supply. These can cause crashes and even permanent damage to computers. Computers and other electronic equipment should really include some kind of over-voltage protection in its mains input to prevent such damamge.

[Jargon File]

Power Mac


Apple Computer's personal computer based on the PowerPC, introduced on 1994-03-14.

The Power Mac G4 (Quicksilver 2002) was the first Power Mac to clock at 1 GHz. In mid-2003, the Power Mac G5 was released, the first Mac to be based on a 64-bit architecture. IBM manufactured the CPU for this new model. The clock speed was initially 1.6 GHz but a dual 2 GHz system was available in September. Existing 680x0 code (both applications and device drivers) run on Power Mac systems without modification via a Motorola 68LC040 emulator. The performance of these unmodified applications is equivalent to a fast 68040-based Macintosh, e.g. a fast Macintosh Quadra.

The Power Mac runs Macintosh operating system from System 7.5 to Mac OS 8.5.

Power Mac Home.

Last updated: 2003-11-26

Power Macintosh

Power Mac

power-on reset


(POR) The processes that take place when a hardware device is turned on. This may include running power-on self-test or reloading software from non-volatile storage. The term implies that the device has some reasonably complex internal state that will be set back to a "normal" initial condition. This state may include the physical state of the device (e.g. a printer) as well as data in the memory of an embedded system.

If a device has no reset button, and sometimes even if it does, turning it off and on again (power cycling) may be the only way to clear a fault.

Last updated: 2012-02-09

power-on self-test

<hardware, testing>

(POST) A sequence of diagnostic tests that are run automatically by a device when the power is turned on.

In a personal computer a typical POST sequence does the following:

- checks that the system board is working

- checks that the memory is working

- compares the current system configuration with that recorded by the PC's configuration program to see if anything has been added or removed or broken

- starts the video operation

- checks that the diskette drive, hard disk drive, CD-ROM drive, and any other drives that may be installed are working.

When POST is finished, typically it will beep, and then let your operating system start to boot. If POST finds an error, it may beep more than once (or possibly not at all if it is your PC speaker that is broken) and display a POST error message. These messages are often nothing more than a single ominous number. Some common numbers and their meanings are:

161 Dead battery (get a new battery for the system board)

162 Configuration changed (you added some memory or a new card to the PC)

301 Keyboard error (take the book off the corner of the keyboard)

Because a successful POST indicates that the system is restored to known state, turning the power off and on is a standard way to reset a system whose software has hung. Compare 120 reset, Big Red Switch, power cycle.

Last updated: 2001-03-30


The PowerOpen Association defines and promotes the PowerOpen Environment (POE).

PowerOpen Association

An independent body established to promote, and test conformance with, the PowerOpen Environment (POE).

Last updated: 1994-11-08

PowerOpen Environment

<operating system>

(POE) A definition containing API and ABI specifications based on the PowerPC architecture. It is not an operating system. The presence of the ABI specification in the POE distinguishes it from other open systems (POSIX, XPG4, etc.) since it allows platform independent binary compatibility which is otherwise typically limited to particular hardware.

The POE is an open standard, derived from AIX and conforming to industry open standards including POSIX, XPG4 and Motif. The POE specification will be publicly available to anyone wishing to produce either application programs or hardware platforms. The PowerOpen Association will provide the necessary conformance testing and POE branding.

The POE is hardware bus independent. System implementations can range from laptop computers to supercomputers. It requires a multi-user, multitasking operating system. It provides networking support, an X Window System extension, a Macintosh Application Services extension and Motif. It is conformance tested and certified by an independent party (the PowerOpen Association).

The POE specification is targeted for availability in the first quarter of 1994. The PowerOpen Association will soon have some of the information material available on-line.

Last updated: 1994-11-08


<processor, standard>

(PPC) A RISC microprocessor designed to meet a standard which was jointly designed by Motorola, IBM, and Apple Computer (the PowerPC Alliance). The PowerPC standard specifies a common instruction set architecture (ISA), allowing anyone to design and fabricate PowerPC processors, which will run the same code. The PowerPC architecture is based on the IBM POWER architecture, used in IBM's RS/6000 workstations. Currently IBM and Motorola are working on PowerPC chips.

The PowerPC standard specifies both 32-bit and 64-bit data paths. Early implementations were 32-bit (e.g. PowerPC 601); later higher-performance implementations were 64-bit (e.g. PowerPC 620). A PowerPC has 32 integer registers (32- or 64 bit) and 32 floating-point (IEEE standard 64 bit) floating-point registers.

The POWER CPU chip and PowerPC have a (large) common core, but both have instructions that the other doesn't. The PowerPC offers the following features that POWER does not:

Support for running in little-endian mode.

Addition of single precision floating-point operations.

Control of branch prediction direction.

A hardware coherency model (not in Book I).

Some other floating-point instructions (some optional).

The real time clock (upper and lower) was replaced with the time base registers (upper and lower), which don't count in sec/ns (the decrementer also changed).

64-bit instruction operands, registers, etc. (in 64 bit processors).

See also PowerOpen, PowerPC Platform (PReP).

IBM PPC info.

gopher://info.hed.apple.com/, "Apple Corporate News/" (press releases), "Apple Technologies/" and "Product Information/". gopher://ike.engr.washington.edu/, "IBM General News/", "IBM Product Announcements/", "IBM Detailed Product Announcements/", "IBM Hardware Catalog/".

Usenet newsgroups: comp.sys.powerpc, comp.sys.mac.hardware.

["Microprocessor Report", 16 October 1991].

Last updated: 1994-09-30

PowerPC 601


A 32-bit RISC processor with 2.8 million transistors (~1.2 million in the core logic) and 32 kilobytes of on-chip cache. Die size: 118.8 mm2. Heat dissipation at 66MHz: 9W. Performance at 66MHz: integer >60 SPECint92, floating-point >80 SPECfp92. Estimated manufacturing cost: $76. Maximum instructions per cycle: 3. 32 32-bit general-purpose registers. 32 64-bit floating-point registers. Successors: PowerPC 603, 604, 620.

Last updated: 2000-01-12

PowerPC G3


A processor chip from Apple Computer, Inc..

Described by Apple as "the third generation in the development of advanced processor technology" the first PowerPC G3 products were launched in 1997. It is specifically optimised for the Macintosh Operating System and uses backside cache to improve performance. The PowerPC G3 has been used by Apple in notebook, desktop and server products.


Last updated: 1998-10-03

PowerPC Platform

<architecture, standard>

(PPCP, PReP - PowerPC Reference Platform, formerly CHRP - Common Hardware Reference Platform) An open system standard, designed by IBM, intended to ensure compatibility among PowerPC-based systems built by different companies. The PReP standard specifies the PCI bus, but will also support ISA, MicroChannel and PCMCIA.

PReP-compliant systems will be able to run the Macintosh OS, OS/2, WorkplaceOS, AIX, Solaris, Taligent and Windows NT. IBM systems will (of course) be PReP-compliant. Apple's first PowerPC Macintoshes will not be compliant, but future ones may be.

IBM info.


[Current OS statuses?]

Last updated: 1997-03-23

PowerPC Reference Platform

PowerPC Platform


<graphics, tool>

A Microsoft application for creating presentations, speeches, slides, etc.

Last updated: 1996-08-26

power save mode


A feature of a component or subsystem designed to actively reduce its power consumption when not in use. Almost any electronic device might benefit from having a power save mode but the most common application is for portable computers which attempt to conserve battery life by incorporating power saving modes in the CPU, display, disks, printer, or other units.

Last updated: 1995-10-14



The powerset of a set S is the set of possible subsets of S, usually written PS.

Last updated: 1994-11-08

Powersoft Corporation


A leading vendor of client/server application development tools.

In February 1994, Watcom became a wholly-owned subsidiary of Powersoft Corporation which merged with Sybase on 13 February 1995. In April 1995, the new company is the fastest growing top-ten software company and the seventh largest software company in the world.


Headquarters: Concord, Massachusetts, USA.

Last updated: 1995-12-27

power supply

power supply unit

power supply unit


(PSU) An electronic module that converts high voltage (110 or 240 VAC) alternating current mains electricity into smoothed direct current at the various differnt voltages required by the motherboard; internal peripheral devices, cheifly storage devices: hard disks, CD or DVD, floppy disks and external connections such as USB. A PSU needs a high enough power output rating to supply all the devices connected to it and should output as little as possible electrical noise, both on the output wires and as electromagnetic radiation.

See also uninterruptable power supply.

Last updated: 2007-09-20

Nearby terms:

pnambicPNGPNPPNU-PrologPOAPoBPOCPOCALpocket calculator

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