P2P (peer-to-peer)
A style of networking in which computers communicate directly with each other rather than depending on interactions managed via central servers and networks. A new generation of highly scalable P2P applications has emerged to handle a variety of spontaneous communications, including:

P3P (Platform for Privacy Preferences Project)
A standard for privacy and content personalization proposed by the World Wide Web Consortium. P3P creates a language in which Web sites and Web users can communicate, and which shields reader preferences and interests.

packet
An information block identified by a label at Layer 3 of the Open Systems Interconnection (OSI) network model (see OSI). It is a collection of bits that contains both control information and data, and is the basic unit of transmission in a packet-switched network. Control information is carried in the packet, along with the data, to provide for such functions as addressing sequence, flow control and error control at each of several protocol levels. A packet can be of fixed or variable length, but generally has a specified maximum length.

packet switching
A technique in which a message is broken into smaller units called packets, which may be individually addressed and routed through the network, possibly using several different routes. The receiving-end node ascertains that all packets are received and in the proper sequence before forwarding the complete message to the addressee.

PACS (picture archiving and communication system)
A type of medical system that provides for the storage and management of digital images, as well as the management of workflow within the radiology department.

PAD (packet assembler/disassembler)
Equipment that serves an entry/exit point for X.25 networks; it assembles packets from the data waiting to be transmitted from the terminal and disassembles packets that have been received from the X.25 link. See X.25.

PAL (Phase Alternate Line)
A color television broadcasting system developed in West Germany and the United Kingdom that uses 650 picture lines and a 50-hertz field frequency. See NTSC (National Television System Committee) and SECAM (Sequential Couleur a Memoire).

PAL (programmable array logic)
A type of programmable logic device (PLD) that consist of an array of "and" gates, called product terms, connected to an array of "and" gates or fixed "or" gates. These devices are capable of providing up to two levels of logic without using additional input/output cells or pins. See PLD.

Palm
This brand name refers to Palm Inc.'s line of PDA devices, as well as its operating-system platform, the Palm OS. Palm once dominated the PDA market with an estimated 80 percent market share, but competitive platforms such as Symbian and Windows CE emerged in 2000. (See PDA, Symbian and Windows CE.)

PAM (pulse amplitude modulation)
The encoding of information in a signal based on the fluctuation of carrier waves. The amplitude of the pulse carrier is varied in accordance with successive samples of the modulating signal.

PAN (personal-area network)
A network in which personal devices or applications dynamically locate and interact with one another. Bluetooth and Jini are examples of emerging PAN technologies. Gartner believes the lifestyle impact of PANs — together with other emerging technologies, such as flexible displays and speech recognition — will be enormous within the next 10 years, leading to a fundamental rethinking of how personal communications and information technology are used in people's everyday lives.

PAP (Password Authentication Protocol)
A security protocol that uses password authentication to allow access to a network or host. In the PAP authentication procedure, an ID/password pair is repeatedly sent by the client to the host until verification is received. Unlike Challenge Handshake Authentication Protocol (CHAD), PAP does not use encryption. See CHAD.

parallel processing
A computing architecture that uses multiple processors operating in parallel. Gartner Dataquest defines parallel-processing configurations that use 32 or more processors as massively parallel processing (MPP) systems. See MPP.

Parallel Sysplex
The cornerstone of IBM's mainframe clustering technology. It is designed to allow multiple central electronics complexes (CECs) to share a common database so a transaction can execute on one of several processors that share a single view of the data. This implementation substantially improves parallelism, and therefore overall system throughput, at a multitasking level. See clustering and CEC.

parallel transmission
Simultaneous transmission of a data stream over multiple channels, or on different carrier frequencies on one channel. See serial transmission.

PARC (Palo Alto Research Center)
Xerox research center famed for having developed the first graphical user interface (GUI) in the 1970s.

PA-RISC (Precision Architecture Reduced Instruction Set Computer)
Hewlett-Packard's reduced instruction set computer (RISC) processor architecture. See RISC.

parity bit
A check bit appended to an array of binary digits to make the sum of all the binary digits, including the check bit, always odd or always even.

partition
As a noun or verb, this term usually refers either to division of application or logic or data over multiple computers, or to the division of a single computer or disk into multiple segments, each running like an independent system.

password
A code used to restrict access to database and other sources of computerized information. With the explosion of the Internet, passwords are becoming the security measure of choice to guard against unauthorized access to protected areas. Unfortunately, the same reasons that make passwords a popular security measure — easy distribution and administration — also make them undependable. Other procedures, such as certification processes used in combination with passwords, provide better security for critical interactions.

PBM (pharmacy benefits management)
A category of healthcare services that involves the managing the delivery of pharmacy and drug-related benefits for members of a managed care or payer plans.

PBN (policy-based networking)
The application of business rules to govern network performance.

PBX (private branch exchange)
A telephone switch (also known as a PABX, or private automatic branch exchange) located on a customer's premises that primarily establishes voice-grade circuits — over tie lines to a telephone company central office (CO) — between individual users and the public switched telephone network. The PBX also provides switching within the customer premises local area, and usually offers numerous enhanced features, including least-cost routing and call detail recording. See CO.

PC (personal computer)
A microcomputer designed primarily for individual use. Sharing resources with another computer is optional. The first PCs were introduced in the late 1970s.

PCB (printed circuit board)
A flat board made of fiberglass or plastic, on which chips and electronic components are interconnected via copper pathways. The primary PCB in a system is called a system board or motherboard, while smaller ones that plug into the slots in the main board are called riser boards or cards.

PC Card
A standard of the Personal Computer Memory Card International Association (see PCMCIA).

PC-DOS
The original operating system that IBM supplied with its personal computers, licensed from Microsoft.

PCI (Peripheral Component Interconnect)
The industry standard system bus architecture that is used in most desktop and server models. PCI provides faster communications between the processor and components (such as memory, disk and video) than the original IBM bus, Industry Standard Architecture (ISA). See ISA.

PCL (Printer Control Language)
The set of commands used by Hewlett-Packard and compatible printers to govern how a document will be printed. PCL is similar to, but less powerful and complex than, PostScript. (See PostScript.)

PCM (patient care management)
A category of systems that enroll or assign patients to interventions across the continuum of health and illness. These include wellness exams and routine screenings, utilization reviews, event focus, short-term case management, and the management of long-term chronic conditions.

PCM (plug-compatible manufacturer)
A hardware vendor whose products are direct replacements for the products of another computer system manufacturer. Initially PCMs provided peripherals that were "plug-for-plug" compatible with IBM peripherals, but the PCM industry has since grown to include IBM-compatible mainframes, and the systems and peripherals of other vendors.

PCM (pulse code modulation)
A digital technique that involves sampling an analog signal at regular intervals and coding the measured amplitude into a series of binary values, which are transmitted by modulation of a pulsed, or intermittent, carrier. It is the standard modulation technique used in telecommunications transmission. See modulation.

PCMCIA (Personal Computer Memory Card International Association)
A nonprofit trade association founded in 1989 to standardize the PC card. The PCMCIA standard has since been renamed the PC Card standard. The standard cards are removable modules that can hold memory, fax/modems, radio transceivers, network adapters, solid-state disks or hard disks in personal digital assistants and other lightweight or portable systems.

PCN (personal communications network)
A defunct term that was originally used for Global System for Mobile Communications (GSM) 1800 networks in Europe. See GSM.

PCO (physician contracting organization)
A legal entity representing multiple physicians, practices and clinics that contracts with other entities to provide healthcare services.

P-code
An intermediate representation of a program that is file-format-independent and is executed by a virtual machine interpreter.

PCR (peak cell rate)
An asynchronous transfer mode (ATM) parameter used to determine the maximum number of cells permitted in a specified time period. See ATM.

PCS (personal communications services)
A low-power, high-frequency digital cellular technology. It operates in the 1.5 to 1.8 gigahertz (GHz) range. In the United States, PCS also operates at 1.9 GHz.

PC/SC (Personal Computer/Smart Card)
Microsoft's specification for using smart cards with PCs. To help forge standards and develop the integration of smart cards and PCs, Microsoft founded the PC/SC Workgroup with other smart card and technology industry companies, including Schlumberger, Hewlett-Packard and Groupe Bull.

PCX (private communications exchange)
A high-capacity evolution of the digital private branch exchange (PBX), which incorporates a cell-based switching fabric or asynchronous transfer mode (ATM) interfaces, an open client/server architecture and a high dependence on computer telephony integration (CTI) to deliver advanced functionality while retaining enterprise investments in PBX line cards and terminal equipment. See PBX, ATM and CTI.

PDA (personal digital assistant)
A handheld computer that serves as an organizer and electronic notepad. It typically uses a stylus or pen-shaped device for data entry and navigation. Types of PDA include clamshell (a computer system that weighs less than 3 pounds and opens lengthwise to expose a keyboard and screen) and tablet (a computer system that weighs less than 4 pounds and that is operated by direct screen contact via a pen or touch interface).

PDC (personal digital cellular)
A Japanese standard for mobile telephony in the 800- to 1,500-megahertz spectrum.

PDF (Portable Document Format)
An Adobe document format that is based on its PostScript page description language, with some major changes. PostScript allows operators to describe a page layout independent of computer platform, device and resolution. PDF has substantially all of PostScript's cross-platform graphic capabilities, but treats each element in a job as a separate object. Modification and proofing of print publication data can be done more easily with PDF than with PostScript. Raster image processor outputs can easily be generated one page at a time via PDF conversions to PostScript. In addition, PDF is emerging as a de facto industry standard for a wide range of context-sensitive document management and electronic-form applications. PDF files must be viewed through Adobe Acrobat installed on a client device.

PDH (Plesiochronous Digital Hierarchy)
The initial structure for organizing the hierarchy or possible bit rates in synchronous time-division multiplexing. It is now superseded by Synchronous Digital Hierarchy (SDH). PDH is defined by the International Telecommunication Union's G.703 standard. See SDH.

PDL (page description language)
The programming language used to specify the way a document will be printed or displayed.

PDM (product data management)
A category of information systems that evolved from the need to better manage paper, electronic documents, engineering change orders, and bills of materials during the product development process. PDM technologies and products have historically been positioned as the primary application backbone for managing and controlling the flow of design intent across the three major design stages: concept design, detail design and production. But in practice, PDM has served as a complementary application tower to computer-aided design (CAD) and enterprise resource planning (ERP) systems by providing the main repository for production-approved engineering data and managing the changes to production-approved data (such as engineering change orders and configuration management). PDM is a key enabler for constructing a concurrent art-to-product environment (CAPE) for enterprisewide design and production. See CAD, CAPE and ERP.

peering
The process by which Internet service providers or other network providers exchange traffic between their customers, based on mutual agreements.

Pentium
The brand name for a series of Intel microprocessors used in IBM-compatible PCs. The original Pentium chip was introduced in 1993 as the successor the 80486 processor, and was based on the same architecture (the "Pentium" name was meant to suggest the number five, as it was the fifth processor in the 80x86 series). Subsequent Pentium-branded Intel processors, each offering progressively advanced performance, include Pentium Pro (1995), Pentium II (1997), Pentium III (1999) and Pentium 4 (2002).

Performance Management

Performance management is the combination of management methodologies, metrics and IT (applications, tools and infrastructure) that enable users to define, monitor and optimize results and outcomes to achieve personal or departmental objectives while enabling alignment with strategic objectives across multiple organizational levels (personal, process, group, departmental, corporate or business ecosystem).

Peripheral Component Interconnect (see PCI)

peripheral
As a noun, a piece of electronic equipment — such as a monitor, keyboard or external disk drive — that is connected to a computer (short for "peripheral device").

PERL (Practical Extraction Report Language)
A Unix scripting language for high-level system control, often used to manage Web servers.

perpetual license
A software license that grants the right to use that software version in perpetuity, with no upgrades included in the price and no fee charged for maintenance. See term license.

personalization
The tailoring of a product, communication or service to an individual customer, or segment of customers, by using knowledge of that customer or segment. Personalization takes four primary forms:

PERT (Program Evaluation and Review Technique)
A management tool for graphically displaying projected tasks, milestones, schedules and discrepancies.

PES (Parallel Enterprise Server)
A label used by IBM for its CMOS-based mainframes.

PFM (personal financial management)
A category of desktop applications used to manage personal finances. Examples include Intuit's Quicken and Microsoft Money.

PFS (patient financial system)
Applications that collect service charges for healthcare services rendered to produce a patient bill and medical claim.

PGA (pin grid array)
An interconnection system for getting electrical signals into and out of a large integrated circuit, such as a microprocessor.

PGP (Pretty Good Privacy)
Public-key encryption software sold by Network Associates. PGP began as an open standard for message encryption. Add-ons are available for a number of desktop products. The underlying protocol has been designated a military weapon by the United States and some other countries in an effort to regulate its distribution, but similar software is widely available on the Internet.

PGS (proposal generation system)
A tool (also known as a "proposal generator") that enables salespeople to quickly develop proposals or other sales documents, such as purchase orders, contracts and quotes.

phase modulation
One of three ways of modifying a sine wave signal to make it carry information. The sine or "carrier" wave has its phase changed in accordance with the information to be transmitted.

PHR (personal health record)
A concept for capturing, managing and sharing a consumer's healthcare profile. Components of a PHR include a consumer profile, a healthcare providers' section, a healthcare encounter section, a family history section and an emergency profile.

PHS (Personal HandyPhone System)
A Japanese standard for digital cellular service. It provides low-mobility or fixed wireless access in the 1,900-megahertz radio band.

physical layer
The lowest layer in the Open Systems Interconnection (OSI) network model. The physical layer addresses the electrical and mechanical procedures associated with the interface that connects a device to a transmission medium. See OSI.

PIM (personal information manager)
Software that organizes and manages random information for fast retrieval on a daily basis. It provides a combination of features, such as a telephone list with automatic dialing, calendar and scheduler.

PIN (personal identification number)
A numeric code — typed on an automated teller machine or telephone keypad, or a computer keyboard — used to gain access to personal funds or information.

ping
A network procedure that sends out a signal and "listens" for an "echo" to determine whether a network-attached device is active.

PIP (packaged integrating process)
A packaged combination of integration middleware components configured for a specific business process. PIPs are separately priced bundles that include everything necessary to integrate specific business processes, including process-specific logic and a runtime integration infrastructure.

PIP (partner interface process)
A feature of the RosettaNet Implementation Framework (RNIF). PIPs define business processes between trading partners. See RosettaNet and RNIF.

pixel
The smallest resolvable dot in an image display.

PKCS (Public Key Cryptography Standards)
A set of security standards from RSA Security. PKCS standards define the cryptographic processes needed to carry out encrypted exchanges between entities.

PKI (public-key infrastructure)
The techniques necessary to manage public-key cryptography (see separate entry), as well as the various systems for authentication, nonrepudiation and integrity that can be built on top of a public-key system.

PKIX (Public-Key Infrastructure Exchange)
An initiative, led by the Internet Engineering Task Force's Public-Key Infrastructure Exchange (PKIX) subcommittee, addressing interoperability and cross-certification among certificate authorities.

PL/1 (Programming Language 1)
An early scientific programming language.

platform
A hardware or software architecture, or an operating system.

platform-independent
A term describing software that can run on a variety of hardware platforms or software architectures. Platform-independent software can be used in many different environments, requiring less planning and translation across an enterprise. For example, the Java programming language was designed to run on multiple types of hardware and multiple operating systems.

PLD (programmable logic device)
A type of application-specific integrated circuit (ASIC) that can be customized by the end user after assembly. See ASIC.

PLM (Product Lifecycle Management)
A product development and management product from SAP.

PL/SQL (Programming Language/Structured Query Language)
An Oracle version of Structured Query Language (SQL) that handles database management system stored procedures.

plug-in
A program that uses a Web browser's application programming interface. Each plug-in is browser- and platform-specific. Plug-ins are stored locally, on the same machine as the browser. The best-known plug-ins are those that allow the display or playback of special file types (such as animation, audio or video) directly in the browser window.

PMOS (p-channel metal-oxide semiconductor)
A semiconductor manufacturing process.

Pocket PC
A personal digital assistant (PDA) platform launched by Microsoft and several partner hardware vendors in April 2000. Pocket PCs, which work with Microsoft's Windows CE operating system, represent a major initiative to gain a major share of the PDA market, once dominated by the Palm-compliant devices, which run the Palm OS operating system. See PDA, Windows CE and Palm.

POCSAG (Post Office Coding Standards Advisory Group)
A standard for radio paging formulated by the British Post Office in 1982, and subsequently adopted by the International Telecommunication Union as a pan-European standard.

POD (print on demand)
A technique that allows an enterprise to print a quantity of documents electronically as needed. Typically, the documents are forms, brochures, booklets or similar documents that formerly had to be printed in large quantities in advance, and stored in a warehouse.

POE (physician order entry)
A category of applications or functions that capture orders from physicians for entry into a healthcare information system.

point to point
Describes a circuit that connects two points directly, where there are generally no intermediate processing nodes, although there could be switching facilities. See multipoint.

polling
A means of controlling communications lines. When many stations are connected to the same circuit, polling from the center is used to ensure an orderly flow of data to the central location. Polling is an alternative to contention that ensures that no terminal is kept waiting for a long time.

polymorphism
The capability of an operation to accept arguments of different or unknown types. Parametric polymorphism executes the same operation on different types. Overloading polymorphism selects appropriate operations according to the type.

PON (passive optical network)
A fiber-based access system to customer premises — for the delivery of video services such as video-on-demand — that allows multiplexed traffic to be distributed to a number of users in such a fashion as to limit the number of optical terminations required.

POP (point of presence)
The point to which the local telephone company terminates subscribers' circuits for access to long-distance service, or to dial-up leased-line or Internet communications.

POP (Post Office Protocol)
An application protocol that provides a mailbox-retrieval service for Internet PC users. It is being replaced by Internet Message Access Protocol (IMAP). See IMAP.

port
The entrance or physical access point to a computer, multiplexer, device or network, where signals may be supplied, extracted or observed.

portal
A public portal is a high-traffic Web site with a wide range of content, services and vendor links. An enterprise portal is a Web-based presentation and interaction interface for users of enterprise applications and resources. Enterprise portals provide windows into enterprise information, applications and processes.

porting
Modifying code that runs on one hardware platform or operating system so that it will properly execute on another hardware platform or operating system.

portlet
A mechanism used to readily integrate content, applications and processes into portals. Portlets provide a low-level, point-to-point integration approach by accessing program application programming interfaces, Structured Query Language statements, Web services and more. Web services and Java provide mechanisms for enabling portlets written for one vendor's portal to run unchanged in another

vendor's portal. Emerging standards to enable portlet interoperability include Java

Specification Request (JSR) 168 and Web Services for Remote Portlets (WSRP). See

portal, JSR 168 and WSRP.

POS (point of sale)
A category of systems that use personal computers or specialized terminals in combination with cash registers, optical scanners or magnetic-stripe readers to capture and record data at the time of transaction. POS systems are usually online to a central computer for credit checking and inventory updating. Alternatively, they may be independent systems that store daily transactions until they can be transmitted to the central system for processing.

POS (point of service)
A type of health maintenance organization (HMO) plan that offers limited coverage for care received outside the HMO's network.

Posix
A Unix-based standard developed by the Institute of Electrical and Electronics Engineers' Posix committee.

PostScript
A page description language (PDL) developed by Adobe Systems. See PDL.

POTS (plain old telephone service)
An informal term for traditional voice-grade communication systems.

ppm (pages per minute)
A measure of document output speed.

PPM (project portfolio management)
A strategy for oversight of a portfolio of related or interdependent projects, with the intent of limiting duplicate work efforts and leveraging decision making and skills across projects. PPM takes a holistic view of projects and their relationships, and focuses on the potential for project benefits to be leveraged across the enterprise. PPM tools, which support this strategy, are high-end, multiproject management tools with:

PPO (preferred provider organization)
An organization offers healthcare services from a select group of "preferred providers" at reduced cost. Access to healthcare services from providers outside the PPO network is available, but the PPO customer must share more of the cost of such services.

PPP (Point-to-Point Protocol)
A standard for communicating over the Internet, or any Internet Protocol network. PPP is specified in request for comments 1331 from the Internet Engineering Task Force.

PPRC (Peer-to-Peer Remote Copy)
A remote-copy capability offered in IBM storage products. It uses standard Enterprise Systems Connection (ESCON) links to communicate between control units. See ESCON.

PPTP (Point-to-Point Tunneling Protocol)
A Microsoft extension to Point-to-Point Protocol (PPP), used to create multiprotocol virtual private networks (VPNs) via the Internet. See PPP and VPN.

predictive modeling
Data mining that uses pattern recognition, statistical and mathematical techniques on large amounts of data to support decision-making by forecasting the outcomes of different scenarios. See data mining.

presentation layer
In the Open Systems Interconnection (OSI) model, the layer of processing that provides services to the application layer, enabling it to interpret the data exchanged, as well as to structure data messages to be transmitted in a specific display and control format. See OSI.

PRI (Primary Rate Interface)
An Integrated Services Digital Network (ISDN) interface that connects private branch exchanges (PBXs) to the network at the North American 1.544 megabits per second (Mbps) T1 rate. It is electrically identical to the ISDN Basic Rate Interface (BRI). North American standards for this interface specify 23 64-kilobit-per-second (Kbps) B, or bearer, channels, plus one 64-Kbps D, or delta, channel. Thus, it is also referred to as 23B+D. In Europe, where it is known as Primary Rate Access (PRA), standards call for 30B+D. See PBX, ISDN and T1.

prime contractor
An outsourcing model in which one organization manages and integrates multiple providers (for example, for products, projects and services) to derive a single or global solution or service for the client.

PRINCE (Projects in Controlled Environments)
A public domain standard for IT developers for the U.K. government. PRINCE provides a process model to define what is involved in setting up, managing and closing down each stage of a project. The model specifies eight components for creating a project management environment: organization, planning, control, risk, stages, quality, change control and configuration management.

private key
The confidential half of the asymmetric key pair used in public-key cryptography. Unlike the "secret key" used in symmetric-key cryptography — a single key known by both the sender and the receiver — a private key is known only by the recipient. See public-key cryptography and secret-key cryptography.

PRM (partner relationship management)
The customer relationship management (CRM) element that extends sales, marketing, customer service and other enterprise business functions to partners to foster more-collaborative channel partner relationships.

problem management
The core function of a customer service and support (CSS) application used by call centers. It coordinates a multitier, multiowner service and support environment, enables pattern analysis, provides management reports, and facilitates requesting additional service and support resources by providing data on the service workload and its changing nature. Because problem management tools can also track service-level agreements, they are valuable for monitoring compliance. See CSS and call center.

process control
In manufacturing systems, the regulation of variables that influence or control the conduct of a process so that a specified quality and quantity of products are obtained. See SPC (statistical process control).

process manufacturing
Manufacturing that adds value by physically or chemically transforming materials, or by extracting, mixing, separating or forming materials, in batch or continuous production modes. Examples include the chemicals, primary metals, printing, and food and beverage industries. See discrete manufacturing.

procurement
All activities concerned with the acquisition of goods and services, including ordering, negotiations and delivery.

PROFS (Professional Office System)
An IBM office system for the Virtual Machine (VM) environment. See VM.

program
An organized list of instructions that, when executed, causes a computer to behave in a predetermined way. Without programs, computers are useless. A program is like a recipe that contains a combination of two things:

A variety of programming languages can be used to create this combination of variables and statements. See programming language.

programming language
A defined group of commands and syntax that a program developer uses to write software. Languages range from primitive ones (which are similar to machine code) to high-level languages (which are closer to standard written language and somewhat automated) and have been classified into generations, such as third-generation languages (3GLs) and fourth-generation languages (4GLs). See 3GL, 4GL and separate entries for the following language examples: C, C++, BASIC, FORTRAN, COBOL and Java.

PROM (programmable read-only memory)
A type of read-only memory (ROM) that can be programmed after manufacture. See ROM and firmware.

prompt
A message from a computer that gives instructions to the user.

propagation delay
The period between when a signal is placed on a circuit and when it is recognized and acknowledged at the other end. Propagation delay is of high importance in satellite channels because of the great distances involved.

protocol
A set of procedures in telecommunications connections that the terminals or nodes use to send signals back and forth. Transmission Control Protocol/Internet Protocol (TCP/IP) is the standard protocol for the Internet and related networks such as intranets and extranets. Local-area networks (LANs) often rely on a specific protocols. Networks and systems cannot communicate unless they use the same protocol or make use of a gateway. See LAN, TCP/IP and gateway.

protocol conversion
The process of translating the protocol native to a system into a different protocol, enabling communication with a second system with which the first system would otherwise be incompatible. Protocol conversion can be performed by a dedicated device (such as a protocol converter) or through software loaded onto an existing system, such as a computer or private branch exchange.

protocol stack
A set of interrelated protocols with complementary functions that apply to different areas of network operations, such as the seven levels of the open systems interconnection (OSI) reference model. See OSI.

proxy agent
A network management agent that operates between an unmanaged device and a management system, allowing management by proxy — that is, on behalf of the device.

proxy server
A device that processes and filters all Internet Protocol (IP) packets that are directed to it and decides which protocols and services can be served out of its cache. Proxy servers tend to offer the greatest range of protocol and caching support since they cache Hypertext Transport Protocol (HTTP), File Transfer Protocol (FTP) and, in some cases, streaming content such as audio and video. Each workstation addresses the proxy server directly by setting specific parameters in each browser on each workstation. See HTTP and FTP.

PR/SM (Processor Resource/System Manager)
A mainframe logical-partitioning facility, introduced by IBM in 1988. PR/SM logical partitions (LPARs) enable multiple operating systems (or copies of the same system) to run on one physical central processing unit or complex. See LPAR.

PSA (professional services administration)
The integration of planning, resource management, project management and project accounting for service organizations. PSA vendors base their businesses on software licensing or subscription, mainly to external service providers (ESPs), and often offer resource exchange capability in conjunction with their software. PSA applications offer opportunity management, time-and-expense, invoicing and other features targeted to professional-service firms. Service process optimization (SPO) is a related term, but it encompasses internal service departments as well as ESPs. See SPO.

PSK (phase shift keying)
Phase modulation that uses discrete changes of phase. See phase modulation.

PSLC (Parallel Sysplex License Charge)
A software licensing arrangement available to vendors if the pieces making up their Parallel Sysplex complex have been qualified by IBM. Charges are based on the total machine capacity. See Parallel Sysplex.

PSO (professional services organization)
A unit within a hardware or software vendor that offers professional services to the vendor's customers. Usually, these services focus on the implementation, maintenance or management of the vendor's products.

PSTN (public switched telephone network)
The worldwide network of public voice communication facilities.

PTO (public telecommunications operator)
An organization responsible for providing public telecommunications services in a given country. The term now generally includes mobile operators, as well as the emerging alternative providers of telecommunications services.

PTT (postal, telegraph and telephone)
The national agency responsible for postal, telegraph and telephone services at a governmental level.

public key
The public half of the asymmetric key pair used in public-key cryptography (see separate entry).

public-key cryptography
An encryption technique developed to overcome the limitations of secret-key cryptography (see separate entry). Public key (also called "asymmetric key") cryptography uses two mathematically related keys: A public key to encrypt messages, and a private key to decrypt them. In a public-key system, you communicate privately by encrypting your message using the public key of your intended recipient. Although everyone else knows the recipient's public key, it is useless for decrypting a message encrypted with it. Only the corresponding private key, known only to the recipient, can decrypt the message.

publish and subscribe
A communication pattern (also known as "publish/subscribe") in which information sources "publish" (i.e., send) information to a middleware infrastructure, and information consumers "subscribe" by specifying what kind of information they want to receive from the infrastructure. The middleware must be able to physically transport messages from one or more publishers to one or more subscribers. It also must be "smart" enough to find the proper destinations by matching each message to subscription criteria. This model naturally supports one-to-many or many-to-many communication — in contrast to either message passing or message queuing, both of which mostly (but not entirely) aim at one-to-one communication.

push technology
Software that automates the delivery of information to users. In contrast, the Web is a "pull" environment that requires a user to seek information. In a "push" environment, information is sent to a person proactively, through a Web browser, e-mail, or even voice mail or a pager. In business, push technology can be used for the conveyance of time-sensitive information, like changes in commodity pricing or the introduction of promotional programs to a sales force. Enterprises can employ push technology to communicate externally with their clients or internally with their employees over a network.

PVC (permanent virtual circuit)
A virtual circuit that is pre-defined in routing tables among the various routers and switches in a packet-switched network, rather than being established on a call-by-call basis. See virtual circuit.

PXE (Preboot Execution Environment)
A technology that allows a PC to be controlled in a pre-boot execution state. Part of the Wired for Management (WfM) specification, it is generally used for pristine operating system loads. See WfM.