A unit of information transmitted as a whole from one device to another on a network. In packet-switching networks, a packet is defined more specifically as a transmission unit of fixed maximum size that consists of binary digits representing both data and a header containing an identification number, source and destination addresses, and sometimes error-control data.
PAL
(Phase Alternation by Line standard) The analog television standard for much of Europe, except France, Russia, and most of Eastern Europe, which use SECAM. As with SECAM, PAL is based on a 50-hertz power rate, but it uses a different encoding process. It displays 625 scan lines and 25 frames per second and offers slightly better resolution than the NTSC standard used in the North America and Japan. PAL bandwidth is 5.5 megahertz.
pay per view
(PPV) A revenue-enhancing system in which cable or satellite customers are charged for watching a single movie or event. This system contrasts with premium cable services, which are paid for monthly regardless of usage.
PC 97
The system and peripheral design elements required for a computer to bear the 1997–1998 "Designed for Microsoft® Windows®" logo. PC 97 Hardware Design Guide defines these requirements.
PC 98
The system and peripheral design elements required for a computer to bear the 1998–1999 "Designed for Microsoft® Windows®" logo. PC 98 Checklist, an addendum to PC 97 Hardware Design Guide, defines these requirements.
pin
In DirectShowfilter graphs, a feature of filters that represents the point where a data stream or control connects to a filter. An input pin receives media samples, and an output pin passes media samples to the next filter. Control pins change properties of the filter.
Plug and Play
A design philosophy and set of specifications that describe changes to hardware and software for the personal computer and its peripherals. These changes make it possible to automatically identify and arbitrate resource requirements among all devices and buses on a computer. Plug and Play specifies a set of application programming interface (API) elements that are used in addition to existing driver architectures.
port
Generally, the address at which a device such as a network interface card (NIC), serial adapter, or parallel adapter communicates with a computer. Data passes in and out of such a port. In Internet Protocol (IP), however, port signifies an arbitrary value used by Transmission Control Protocol/Internet Protocol (TCP/IP) and User Datagram Protocol/Internet Protocol (UDP/IP) to supplement an IP address so as to distinguish between different applications or protocols residing at that address. Taken together, an IP address and a port uniquely identify a sending or receiving application or process. See also port driver.
port driver
An interface library of functions and services provided to a minidriver so that the minidriver can communicate with the operating system. The MPEG port driver is one example.
power management
A computer's or device's capability to use less power while remaining on and ready for use. This capability is provided by hardware and supported by operating system software. The state of low power consumption is called the sleeping state. Power management is required in computers and devices that comply with the OnNow initiative, as recommended for a broadcast client.
An on-screen guide that lists television and cable programs and broadcast time slots. This Broadcast Architecture component receives current information about program schedules and maintains these in the Guide database. The Program Guide enables the viewer to review, select, and control what programs will be watched.
pull model
A broadcast model in which a server sends information to clients only upon request. The pull model contrasts with the push model in which a server sends information to one or more clients without waiting for requests. The pull model is more efficient for interactively selecting specific data to receive but uses excessive bandwidth when many clients request the same information.
push model
A broadcast model in which a server sends information to one or more clients on its own schedule, without waiting for requests. The clients scan the incoming information, save the parts they have been instructed to save, and discard the rest. Because the push model eliminates the need for requests, it eliminates the need for a back channel from the client to the server. The push model contrasts with the pull model, in which each client requests information from a server.