Any block of data sent over a network. Each packet contains information about the sender and the receiver, and error-control information, in addition to the actual message. Packets may be fixed- or variable- length, and they will be reassembled if necessary when they reach their destination.
A data transmission method that simultaneously sends data packets from many sources over the same communications channel or telephone line, thus optimizing use of the line.
A specialized chip designed to manage virtual memory.
A memory-management technique used to speed up the performance of dynamic RAM.
In a page-mode memory system, the memory is divided into pages by specialized dynamic RAM chips. Consecutive accesses to memory addresses in the same page results in a page-mode cycle that takes about half the time of a regular dynamic RAM cycle.
An approximation of the number of pages that a laser printer can print in one minute. This number often represents the rate that the printer can reach when printing the simplest output; if you combine text with complex graphics, performance will fail.
A very small battery-powered portable computer that you can hold in one hand, often weighing about a pound.
Presence and Availability Management-API spec. PAM-API is designed for customizing communications services to user's preferences. PAM describes a software platform designed to enable service providers to securely share certain data necessary to deliver advanced, customizable voice and data services that interact across both wired and wireless networks. See http://www.pamforum.org
Many palmtop computers have small screens of 8 lines by 40 characters, and tiny keyboards.
The transmission of information from computer to computer, or from computer to a peripheral, where all the bits that make up the character are transmitted at the same time over a multiline cable.
An input/output port that manages information 8 bits at a time, often used to connect a parallel printer.
Any printer that can be connected to the computer using the parallel port.
A computing method that can only be performed on systems containing two or more processors operating simultaneously.
Parallel processing uses several processors, all working on different aspects of the same program at the same time, in order to share the computational load.
A small part of the Macintosh random-access memory that holds information including the hardware configuration, the date and time, which disk is the startup disk, and information about the state of the Desktop. The contents of PRAM are maintained by a battery, and so the contents are not lost when the Mac is turned off or unplugged at the end of session.
In communications, a simple form of error checking that uses an extra, or redundant bit, after the data bits but before the stop bit(s).
Parity may be set to odd, even, mark, space, or none. Odd parity indicates that the sum of all the 1 bits in the byte plus the parity bit must be odd. If the total is already odd, the parity bit is set to zero; if it is even, the parity bit is set to 1.
In even parity, the sum of all the 1 bits is even, the parity bit must be set to 1; if it is odd, the parity bit must be set to 1.
In mark parity, the parity bit is always set to 1, and is used as the eighth bit.
In space parity, the parity bit is set to 0, and used as the eighth bit.
If parity is set to none, there is no parity bit, and no parity checking is performed.
The parity setting on your computer must match the setting on the remote computer for successful communications. Most online services use no parity and an eight-bit data word.
An extra or redundant bit used to detect transmission errors.
A check mechanism applied to a character or series of characters that uses the addition of extra or redundant bits known as parity bits. Parity checking is used in situations as diverse as asynchronous communications and computer memory coordination.
A mismatch in parity bits that indicates an error in transmitted data.
To move the hardisk read/write heads to a safe area of the disk (called a landing zone) before you turn your system off, to guard against damage when the computer is moved. Most modern hard disks park their heads automatically, and so you do not need to run a special program to park the heads.
A portion of a hard disk that the OS treats as if it were a separate drive.
In DOS,an area of the hard disk containing information on how the disk is organized.
It also contains information that tells the computer which OS to load.
An LCD display mechanism that uses a transistor to control every row of pixels on the screen. This is in sharp contrast to active-matrix screens,where each individual pixel is controlled by its own transistor.
Personal Computer. A computer specifically designed for use by one person at a time, equipped with its own CPU, memory, OS, keyboard and display, hard/floppy disks, as well as other peripherals when needed.
A term describing add-in cards that conform to the PCMCIA standard.
PC Card slot
An opening in the case of a portable computer intended to receive a PC Card; also known as a PCMCIA slot.
The version of the DOS operating system supplied with PCs sold by IBM.
Peripheral Component Interconnect. A specification introduced by Intel that defines a local bus that allows up to ten PCI-compliant expansion cards to be plugged into the computer. One of these ten cards must be the PCI controller card, but the others can include a video card, network interface card,SCSI interface, or any other basic I/O function.
The PCI controller exchanges information with the computer's processor as 32- or 64- bits, and allows intelligent PCI adapters to perform certain tasks concurrently with the main processor by using bus mastering techniques.
Personal Computer Memory Card International Association. A nonprofit association formed in 1989 with over 320 members in the computer and electronics industries that developed a standard for credit-card size plug-in adapaters aimed at portable computers.
A PCMCIA adapter card, or PC Card, uses a 68-pin connector, with longer power and ground pins, so they always engage before the dignal pins. Several versions of the standard have been approved by PCMCIA:
TypeI: The thinnest PC Card, only 3.3mm thick; used for memory enhancements including dynamic RAM, static RAM, and EEPROM.
TypeII:A card used for modems or LAN adapters, 5 mm thick.
TypeIII:A 10.5 mm card, used for mini-hard disks and other devices that need more space, including wireless LANs.
In theory, although space is always a major consideration, each PCMCIA adapter can support 16 PC Card sockets, and up to 255 adapters can be installed in a PC that follows the PCMCIA standard; in other words PCMCIA allows for up to 4080 PC Cards on the same computer.
The majority of PCMCIA devices are modems, Ethernet and Token Ring network adapters, dynamic RAM, and flash memory cards, although mini-hard disks, wireless LAN adapters, and SCSI adapters are also available.
Personal Digital Assitant. A tiny pen-based palmtop computer that combines fax,e-mail,PCMCIA support, and simple word processing into an easy-to-use unit that fits into a pocket.
A computer that accepts handwriting as input. Using a pen-like stylusm, you print neatly on a screen, and the computer translates this input using pattern recognition techniques. You can also choose selections from on-screen menus using the stylus.
Any hardware device attached to and controlled by a computer, such as a monitor, keyboard, hard-disk, floppy-disk, CD-ROM drives, printer, mouse, tape drive, and joystick.
permanent swap file
A swap file that, once created, is used over and over again. This file is used in virtual memory operations, where hard disk space is used in place of random access memory(RAM).
Although it can represent one quadrillion bytes (1015),it usually refers to 1,125,899,906,842,624 bytes (250).
The special electrofluorescent coating used on the inside of a CRT screen that glows for a few milliseconds when struck by an electron beam. Because the illumination is so brief, it must be refreshed constantly to maintain an image.
A real device in the computer that you can see or touch, rather than a logical drive, which is a part of the hard disk that functions as if it were a separate disk drive but is not. One physical drive may be divided into several logical drives.
The first and lowest of the seven layers in the ISO/OSI model for computer-to-computer communications. The physical layer defines the physical, electrical, mechanical, and functional prodedures used to connect the equipment.
A unit of measure used to measure type size. One pica(12 points) is equivalent to 1/6".
A description of a chip or other electronic component with connecting pins exactly equivalent to the connectiong pins used by a different device. This allows for easy system upgrade; you replace the older chip with a newer, more capable version.
A type of distortion that usually occurs at the edges of a video screen where the sides of an image seem to bow inwards.
1. In processor architecture, a method of fetching and decoding instructions that ensures that the processor never needs to wait; as soon as an instruction is executed, another is waiting. 2.In parallel processing, the method used to pass instructions from one processing unit to another.
Contraction of picture element. The smallest element that display software can use to create text or graphics. A display resolution described as being 640x480 has 640 pixels across the screen and 480 down the screen, for a total of 307,200 pixels. The higher the number or pixels, the higher the screen resolution.
A monochrome pixel can ahve two values, black or white, and this can be represented by one bit as either zero or one. At the other end of the scale, true color capable fo displaying approximately 16.7 million colors, requires 24 bits of information for each pixel.
The actual disk inside a hard disk enclosure that carries the magnetic recording material. Many hard disks have multiple platters, most of which have two sides that can be used for recording data.
A peripheral used to draw high-resolution charts, graphs, layouts, an other line-based diagrams, an often used with CAD systems.
A standard that defines automatic techniques designed to make PC configuration simple and straight-forward.PnP adapters contain configuration information stored in non-volatile memory, which includes vendor information, serial number, and checksum information. The PnP chipset allows each adapter to be isolated, one at a time, until all cards have been properly identified by the OS.
PnP requires BIOS changes so that cards can be isolated and identified at boot time; when you insert a new card, the BIOS should perform an auto-configuration sequence enabling the new card with appropriate settings.
Describes any hardware device designed to work in exactly the same way as a device manufactured by a different company.
1.A physical connection, such as a serial port or a parallel port. 2.To move a program or OS from one hardware platform to another. 3.A number used to identify a specific Internet application(location).
A page-description language developed by Adobe Systems,Inc., used when printing high-quality text and graphics.
POST A set of diagnostic programs, loaded from ROM, designed to ensure that the majore system components are present and operating. If a problem is found, the POST software writes an error message in the screen, sometimes with a diagnostic code number indicating the type of fault located. These POST tests execute before any attempt is made to load the OS.
A part of the computer that converts the power from a wall outlet into the lower voltages, typically 5 to 12 volts DC, required internally in the computer. PC power supplies are usually rated in watts, ranging from 90 watts at the low end to 300 watts at the high end. If the power supply in your computer fails, nothing works, not even the fan.
A brief but sudden increase in line voltage, often destructive, usually caused by a neraby electrical appliance such as a photocopier or elevator, or when power is reapplied after an outage.
Point-to-Point Protocol. One of the most common protocols used to connect a PC to an Internet host via high-speed modem and a telephone line.
PPP established a temporary but direct connection to an Internet host, eliminating the need for connecting to an interim system. PPP also provides a method of automatically assigning an IP address, so that remote or mobile systems can connect to the network at any point.
A form of multitasking where the OS executes an application for a specific period of time, according to its assigned priority. At that time, it is preempted, and another task is given access to the CPU for its allocated time. Although an application can give up control before its time is up, such as during input/output waits, no task is ever allowed to execute for longer than its allotted time period.
The sixth of seven layers of the ISO/OSI model. The presentation layer defines the way that data is formatted, presented, converted, and encoded.
In DOS, a division of the hard disk that contains important OS files.
A DOS hard disk can be divided into two partitions, or areas; the primary DOS partition, and the extended DOS partition. If you want to start your computer from the hard disk, the disk must contain an active primary DOS partition that includes the three DOS system files:MSDOS.SYS,IO.SYS,and COMMAND.COM. The primary DOS partition on the first hard disk in the system is referred to as drive C.
Any flat board made of plastic or fiberglass that contains chips and other electronic components. Many PCBs are multi-layer boards with several different sets of copper traces connecting components together.
The ability of a printer to change modes so that it behaves just like a printer from another manufacturer.
A DOS device driver that lets you use code-page switching with printers that support this capability. To activate it, load PRINTER.SYS using CONFIG.SYS
An operating mode supported in protected mode that allows the OS and certain classes of device driver to manipulate parts of the system including memory and I/O ports.
Programmable Read-Only Memory. A chip used when developing firmware. A PROM can be programmed and tested in the lab, and when the firmware is complete, it can be transferred to a ROM for manufacturing.
An operating state that supports advanced features, such as hardware support for multitasking,virtual memory management, and the prevention of programs from accessing blocks of memory that belong to other executing programs
In networking and communications, the specification that defines the procedures to follow when transmitting and receiving data. Protocols define the format, timing, sequence, and error checking systems used.
In networking and communications, the several layers of software that define the computer-to-computer or computer-to-network protocol.
public domain software
Software that is freely, distributed to anyone who wants to use,copy, or distribute it.
A method used to convert an analog signal into noise-free digital data that can be stored and manipulated by computer. PCM takes an 8-bit sample of a 4kHz bandwidth 8000 times a second, which gives 16K of data per second. PCM is often used in multimedia applications.