PAC
Public Access Catalog. The SDSU University Library's on-line catalog which lists the books held here and the journals subscribed to (but not their contents. It also provides information on circulation status, books and journals ordered but not yet received, receipt of journal issues, and more.

Packet
The unit of data sent across a packet switching network. While some Internet literature use the term to refer specifically to data sent across a physical network, other literature views the Internet as a packet switching network and describes IP Datagrams as packets.

Packet-switching
Data transmission process, utilizing addressed packets, whereby a channel is occupied only for the duration of the packet transmission. SDSUnet is a are packet-switching network.

Paint
The oldest and most limited Macintosh graphic file format, holding only black-and-white bit maps at 72 dpi. Paint files (file type PNTG) are limited to 8 by 10 inches.

Parallel Cable/Parallel Port
A cable used to connect peripheral devices through a computer's parallel port. A type of port that transmits data in parallel (several bits side by side).

Parameter
A word, number, or symbol that is typed after a command to further specify how the command should function.

Parity
A check bit used to make the sum of the bits in a unit of data either even or odd (including the parity bit). A unit of data that is 8 bits long would have no parity, and a unit of data 7 bits long would have an even parity bit to make an 8 bit word. Parity is used to check a unit of data for errors during transmission through phone lines or null modem cables.

Paste
To insert information from the Clipboard. Information can be pasted multiple times.

Path
A route used in finding, retrieving, and storing files on a disk. The course leading from the root directory of a drive to a particular file.

PERL
The Practical Extraction and Report Language. An interpreted language for CGI scripts.

PCMCIA
A standard format for credit-card-size expansion cards, used to add features to laptop computers, hand-held computers, and desktop computers. The acronym stands for Personal Computer Memory Card International Association.

PDF
Portable Document Format. A PDF file is an electronic facsimile of a printed document.

Peer-to-peer
A network setup that allows every computer to both offer and access network resources, such as shared files, without requiring a centralized file server. Macintosh computers utilize this type of network setup.

Peripheral
A piece of hardware that's outside the main computer. It usually refers to external hardware such as disk drives, printers, and scanners sold by a third party.

PERL
Practical Extraction and Reporting Language. A robust programming language frequently used for creating CGI programs on web servers.

PICS
The standard macintosh graphic file format for animations. Essentially a collection of bit-mapped PICT images in sequential order, much like movie frames.

PICT/PICT 2
PICT is the standard macintosh graphic file format for graphics that are cut or copied to the Clipboard and for drawings that won't be output on PostScript printers. This format is ideal for on-screen presentations, but page layout programs sometimes have problems with PICT files. Files are sometimes called metafiles because they can contain both bit maps and QuickDraw-based objects.

Pixel
Picture element. Digital images are composed of touching pixels, each having a specific color or tone. The eye merges differently colored pixels into continuous tones.

Pixel Skipping
A means of reducing image resolution by simply deleting pixels throughout the image.

PKZIP/PKUNZIP
A software compression utility for the PC. It allows you to compress or "zip" a file or a number of files into one archive file in the ZIP file format.

Plug-In
Extends the capabilities of a web browser, allowing the browser to run multimedia files.

PMT
Photomultiplier tube. The light sensing device generally used in drum scanners.

POP
A server using the Post Office Protocol, which holds users' incoming e-mail until they read or download it.

Port
One of several rendezvous points where TCP/IP connections can be made on a computer. Ports are numbered, with several locations reserved for specific types of network activity, such as telnet on port 23, HTTP traffic on port 80 and USENET news (NNTP) on port 119.

Posterization
The conversion of continuous tone data into a series of visible tonal steps or bands.

ppi/ppc
Pixels per inch or pixels per centimeter. Units of measurement for scanned images.

PPP
Point-to-Point Protocol. It provides a method for transmitting packets over serial point-to-point links.

PRAM
Parameter RAM (pronounced pee-ram). A small portion of the Mac's RAM set aside to hold basic information such as the date and time, speaker volume, desktop pattern, and key-board and mouse settings. PRAM is powered by a battery, so it doesn't lose the settings when you shut down. Sometimes, however, the PRAM data gets corrupted, causing crashes or other problems.

Primary color
A base color that is used to compose the other colors.

Process Ink Colors
CMYK pigments used in printing processes, chosen to produce the widest range of color mixtures.

Profile
The color characteristics of an input or output device, used by a CMS to ensure color fidelity.

Properties
Information about an object, including settings or options for that object. For example, you look at properties of a file for information such as the file size, file type, and file attributes.

Protocols
When data is being transmitted between two or more devices something needs to govern the controls that keep this data intact. A formal description of message formats and the rules two computers must follow to exchange those messages. Protocols can describe low-level details of machine-to-machine interfaces (e.g., the order in which bits and bytes are sent across wire) or high-level exchanges between application programs (e.g., the way in which two programs transfer a file across the Internet).

Proxy ARP
A technique in which one machine, usually a gateway, answers ARP requests for another machine. By pretending to be the physical network location of another machine, the gateway takes over the responsibility of routing packets destined for the other machine. For instance, a gateway can proxy ARP for addresses that the gateway identifies as being off the local network and that the gateway has a route for. The originating computer receives the gateway's proxy ARP reply and sends the datagram on to the gateway, which routes the datagram to its actual destination network.

PSN
Packet Switch Node; a store-and-forward packet switch (formerly called an IMP).

Public-domain
Software that has no copyright or fee, which means you can copy, use, and even alter and sell it.