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Packet Network segments of data that also include header, destination address, and trailer information.

Page Memory allocated in 4K or 16K segments within a page frame.

Page fault A program interrupt that occurs when an application requests data or instructions stored in virtual memory.

Page frame A 64K upper memory area divided into four equal-sized pages through which the memory manager swaps data.

Page-in The process in which the memory manager goes to the hard drive to return the data from a swap file to RAM.

Page-out The process in which, when RAM is full, the memory manager takes a page and moves it to the swap file.

Parallel Port A port that parallel transmits or receives 8 bits (1 byte) of data at a time between the computer and external devices. Mainly used by printers. The DOS names for parallel ports are LPT1 and LPT2.

Parity An error-checking scheme In which the bits in a byte are added to determine the value of a ninth, or "parity," bit . The value of the parity bit is set to either 0 or 1 to provide an even number of ones for even parity or an odd number of ones for odd parity.

Parity error An error that occurs when the number of 1s in the byte is not in agreement with the expected number.

Parity generator chip A fake parity chip designed to simulate parity checking so that the user can use less expensive nonparity memory modules on a systemboard that expects parity memory. See Fake parity chip.

Parity memory Nine-bit memory in which the 9^th bit is used for error checking. Older DOS PCs almost always use parity chips.

Partition table A table written at the very beginning of a hard drive that describes the number and location of all partitions, and identifies the boot partition.

Passive network A network, such as Ethernet, in which the computers, not dedicated network devices, drive the signals over the network.

PATH command A DOS command that tells the OS where to look for executable files (for example, the PATH command in an AUTOEXEC.BAT file might be PATH C:\DOS;C:\WINDOWS which tells the OS to look for executable files first in the DOS directory and then in the Windows directory).

PC Card Also called PCMCIA card. A credit-card-sized adapter card that can be slid into a slot in the side of many notebook computers and used for connection to modems, networks, and CD-ROM drives.

PC Card slot Also called a PCMCIA card slot. An expansion slot on a notebook computer, into which a PC Card is inserted.

PC-compatible A computer that uses an Intel (or compatible) processor and can run DOS and Windows.

PCB (Printed Circuit Board) A board upon which there are layers of printed circuits and onto which other integrated circuits can be soldered or otherwise attached.

PCI bus (Peripheral Component Interconnect) A bus common on Pentium computers that runs at speeds of up to 33MHz, with a 32-bit-wide data path.

PCI expansion slot (Peripheral Component Interconnect) Slots found on most Pentium systemboards. They can accept 32- or 64-bit adapter cards, and allow the card to interface with the PCI bus.

PCL (Printer Command Language) Usually refers to Hewlett-Packard laser printers. Most H-P compatibles support PCL 4. H-PÆs newest printers (the III series) use PCL 5, which includes scalable fonts and monochrome support for HPGL.

PCM (Pulse code modulation) A method of sampling sound in a reduced, digitized format, by recording differences between successive digital samples instead of their full values.

PCMCIA (Personal Computer Memory Card International Association) A consortium of computer manufacturers that devised the standard for the credit card-size adapter cards used in many notebook computers. PCMCIA defines three card types: Type I cards can be up to 3.3mm thick and are generally used for RAM and ROM expansion cards; Type II cards can be as thick as 5.5mm and typically house modems and fax modems; Type III cards are the largest of the lot (up to 10.5mm thick) and are mostly used for solid state disks or miniature hard disks. PCMCIA cards are also known as 'PC Cards'.

Also See PC Card.

PCMCIA card slot See PC Card slot.

PDA (Personal Digital Assistant) A handheld device that combines computing, telephone/fax, and networking features. A typical PDA can function as a cellular phone, fax sender, and personal organiser. Some PDAs are hand-held PC with tiny keyboards. Another class of device uses a touch-screen and stylus for data entry.

PDC (Primary domain controller) The computer that controls the directory database of user accounts, group accounts, and computer accounts on a Windows NT domain.

Peripheral Any hardware device - such as a disk drive, tape drive, printer or modem - added to a system as a complement to the basic CPU.

Phase-dual or PD optical drives A type of optical hard drive that is rewritable and may store several gigabytes of data, yet can also read traditional CD-ROMs.

Physical layer The OSI layer responsible for interfacing with the network media (cabling).

PIC (Programmable Interrupt Controller) A chip or device that prioritises interrupt requests generated by keyboards, serial ports, and other devices and passes them on to the CPU in order of highest priority. See also IRQ.

Picolitre (pl) A million millionth of a litre.

PIF (Program information file) A file used by a DOS application that describes the environment the DOS program uses. Used in Windows 3.x.

PIM (Personal Information Manager) A type of software application - a given on PDA devices and many mobile phones - that allows you to enter text for any purpose and retrieve it based on any of the words you typed in. PIMs vary widely, but all of them attempt to provide methods for managing information the way you use it on a daily basis. Typical features include a telephone list, calendar, scheduler, reminder and calculation functions.

Pipelined burst SRAM (Pipeline burst cache) A less-expensive SRAM that uses more clock cycles per transfer than non-pipelined burst SRAM, but does not significantly slow down the process.

Pipelining A process that allows a CPU to begin processing a new instruction as soon as the preceding instruction moves to the next stage, thus providing faster throughput.

Pits Recessed areas on the surface of a compact disc, separating Lands. Lands and pits represent data as either a 0 or a 1.

Pixel A pixel is the smallest information building block of an on-screen image. On a color monitor screen, each pixel is made of one or more triads (red, green, and blue). Resolution is usually expressed in terms of the number of pixels that fit within the width and height of a complete on-screen image. In VGA, the resolution is 640 by 480 pixels; in SuperVGA, it is 800 by 600 pixels.

Platter The actual disk inside a hard-disk drive; it carries the magnetic recording material. All but the thinnest disk drives have multiple platters, most of which have two sides that can be used for data storage. (On multiple-platter drives, one side of each platter is usually reserved for storing control information.)

Plug-and-Play BIOS Basic input/ output system for Plug-and-Play devices that are designed to be automatically recognized by the computer upon installation.

PnP (Plug and Play) A Microsoft/Intel specification that allows for self-configuration of computers and peripherals. A fully Plug and Play-enabled PC requires three PnP components: a PnP BIOS, PnP adapters and peripherals, and a PnP operating system. Adding a PnP-compliant device to a PnP PC requires little more than making the physical connection. The operating system, in conjunction with PnP logic present in the BIOS and in the device itself, handles the IRQ settings, I/O addresses, and other technical aspects of the installation to ensure that the device does not conflict with other installed devices.

Polling A process by which the CPU checks the status of connected devices to determine if they are ready to send or receive data.

Polymorphic virus A type of virus that changes its distinguishing characteristics as it replicates itself. Mutating in this way makes it more difficult for AV software to recognize the presence of the virus.

Port The channel or interface between the microprocessor and peripheral devices. e.g. Printer, mouse, external modem……

Port settings The configuration parameters of communications devices such as COM1, COM2, or COM3, including IRQ settings.

Port speed The communication speed between a DTE (computer) and a DCE (modem). As a general rule, the port speed should be about four times as fast as the modem speed.

POSIX (Portable Operating System Interface) A set of standards adopted to allow operating systems (such as Unix and NT) and their applications to port from one platform to another.

POST (Power-on self-test) A self-diagnostic program used to perform a simple test of the CPU, RAM, and various I/O devices. The POST is performed when the computer is first turned on.

Power conditioners Line conditioners that regulate, or condition, the power, providing continuous voltage during brownouts.

Power supply A box inside the computer case that supplies power to the systemboard and other installed devices. Power supplies normally provide between 5 and 12 volts DC.

PPP (Point-to-Point Protocol) A common way PCs with modems can connect to an internet. The Windows Dial-Up Networking utility, found under My Computer, uses PPP.

Presentation layer The OSI layer that compresses and decompresses data and interfaces with the Application layer and the Session layer.

Primary cache See Internal cache.

Printer A peripheral output device that produces printed output to paper. Different typs of printers include dot matrix, ink-jet, and laser.

Protected Mode A memory-addressing system supporting 32-bit instruction sets. I t mediates between different programs running at once, and keeps them within their memory boundaries.

Process An executing instance of a program and its resources. There can be more than one process running for a program at the same time. One process for a program happens each time the program is loaded into memory or executed.

Program A set of step-by-step instructions to a computer. Some are burned directly into chips, while others are written in languages such as BASIC or C++.

Program jump In a program, an instruction that causes control to be sent to a memory address other than the next sequential address.

Proprietary When a company has exclusive rights to manufacture and/ or market a product.

Protected mode A mode used by 80286 and newer systems that can address more than 1MB of memory. It controls memory addresses that a program can access. (Windows 95 runs in protected mode.)

Protocol 1] A set of preestablished rules for communication. Examples of protocols are modem parity settings and the way in which header and trailer information in a data packet is formatted.

2] A formal set of rules and descriptions of information formats that allow two computers to exchange information.

Program See application software

Programming Language Any artificial language that can be used to define a sequence of instructions that can ultimately be processed and executed by the computer.

PROM (Programmable Read-Only Memory) A (usually) permanent memory chip programmed after manufacture (unlike a ROM chip). EPROMs (erasable PROMs) and EEPROMs (electrically erasable PROMs) can be erased and reprogrammed several times.

PS/2 (Personal System 2) An IBM personal computer series introduced in 1987, superseding the original PC line. It introduced the 3.5in floppy disk, VGA graphics and Micro Channel bus. The latter has since given way to the PCI bus.