Glossary of Acronyms

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PB - Pipeline Burst Cache. A type of motherboard cache memory. Pipeline burst consists of one single SIMM of SRAM.

PBSRAM - Pipelined Burst Synchronous RAM - Type of L1 cache memory installed in the Intel Klamath Pentium Pro Processor.

PC. Personal Computer. The original personal computer developed by IBM in 1981 with the 8088 CPU. The PC had no hard drive. Also, any personal computer that is IBM compatible.

PCB - Printed Circuit Board. A system board or add in card that contains a number of chips, sockets, discrete components, and connectors.

P-CHS - Physical CHS. The CHS used at the ATA device interface. This CHS is also used at the INT 13H interface by older BIOS that do not support >1024 cylinders or >528 MB.

PCI - Peripheral Component Interconnect. A local bus developed by Intel being promoted as the successor to VL. This type of device, developed by Intel, is used in most Pentium computers. The PCI bus is a 64 bit interface in a 32 bit package that runs at 33 MHz and can transfer 32 bits of data (four bytes) every clock tick (132 MB per second). Since a clock tick at 33 MHz is 30 nanoseconds, and memory only has a speed of 70 nanoseconds. When the CPU fetches data from RAM, it has to wait at least three clock ticks in the ISA bus for the data. By transferring data every clock tick, the PCI bus can deliver the same throughput on a 32 bit interface that other parts of the machine deliver through a 64 bit path. The PCI bus has all the signals to the old ISA bus. The PCI bus connects at one end to the CPU/Memory bus and at the other end to a more traditional I/O bus.

The PCI bus is a mezzanine bus, divorced from the CPU, giving it some independence and the ability to cope with more devices, so it's more suited to cross-platform work. It is time multiplexed, meaning that address and data lines share connections. It has its own burst mode that allows 1 address cycle to be followed by as many data cycles as system overheads allow. At nearly 1 word per cycle, the potential is 264 Mb/sec. It can operate up to 33 MHz, or 66 MHz with PCI 2.1 and can transfer data at 32 bits per clock cycle so you can get up to 132 Mbytes/sec (264 with 2.1). Each PCI card can perform up to 8 functions, and you can have more than one busmastering card on the bus. It should be noted, though, that many functions are not available with PCI, such as sound. Not yet, anyway. It is part of the plug and play standard, assuming your operating system and BIOS agree, so it is auto configuring (although some cards use jumpers instead of storing information in a chip); it will also share interrupts under the same circumstances. The PCI chip set handles transactions between cards and the rest of the system, and allows other buses to be bridged to it (typically and ISA bus to allow older cards to be used). Not all of them are equal, though; certain features, such as byte merging, may be absent. The connector may vary according to the voltage the card uses (3.3 or 5v; some cards can cope with both).

PCM - Pulse Code Modulation. A technique for converting an analog signal with an infinite number of possible values into discrete binary digital words that have a finite number of values. The waveform is sampled, then the sample is quantified into PCM codes.

PCMCIA - Personal Computer Memory Card International Association. Standard for the credit card size interface cards in portables and other small computers. Essentially assigns IRQ's for portable computers when operating remotely. PCMCIA cards (also known as PC Cards) are credit card sized components that fit into slots to add capabilities such as memory, modems, LAN connections, or serial ports. PC cards enable you to easily install or swap memory and I/O devices used the most. Some of the newest cards are multifunctional, providing, for instance, both a fax/modem and LAN access on one tiny PC Card. Because they are standardized, they are not restricted to a specific make or model of computer.

The Personal Computer Memory Card Association is a non profit standards body chartered with establishing, marketing, and maintaining standards for PCMCIA cards. The PCMCIA standard defines six functional hardware and software standards, being for card slots, the socket/adapter interface, Socket Services, Card Services, Card Information Structure (CIS) , and the system software. The system software reads the CIS data on insertion, installs the appropriate drivers, notifies system resources, and initializes the card to make it available for use by the host. There are three types of PCMCIA slots, and a fourth one is coming soon. Slots are identified by the thickness of the cards that fit in them. All types are backwards compatible because they use the same 68 pin interface, and interface with both 8 and 18 bit buses. They also support physical access of up to 64 MB of memory.

Type I Cards - Are 3.3 mm thick, and are used primarily in PDAs and other handheld devices for extra RAM, FLASH memory, electrically erasable programmable read only memory (EEPROM), and one time programmable memory devices.

Type II Cards - Are 5 mm thick and are fully I/O capable. They're used primarily for PC enhancements such as memory, modems, LAN connections, and host communications.

Type III Cards - Are 10.3 mm thick. They're designed primarily for removable hard drives which require a larger size.

Type IV Cards - Have not yet been ratified by the PCMCIA consortium but are expected to be 18 mm thick and will be used for large capacity hard drives.

PCMCIA cards are plugged into a host socket/adapter on the computer's motherboard or connected to an expansion bus. The socket side has the standard 68 pin interface for the card. The adapter side translates the PCMCIA interface signals to match he computer's bus standards. Socket Services is the software interface between the card in the socket and the adapter to the computer's bus. The standard Socket Services interface is what permits the use of any PCMCIA card on any PC equipped with a socket/adapter.

The programming interface for PCMCIA is called Card Services. It sends the signals to link Socket Services to the PC's operating system and hardware. Card Services can be implemented either as a driver, or in the operating system as is IBM DOS 6.0. Card Information Structure (CIS) contains information about how the card functions, its size, its electrical requirements, and so on. On card insertion, the card passes this identifying information to the host system. The system software reads the CIS data on insertion, installs the appropriate drivers, notifies system resources, and initializes the card to make it available for use by the host.

PDA - Personal Digital Assistant. A handheld computer that can be programmed with software from multiple vendors.

PEl - Pixel. A picture element, the smallest addressable unit of a graphical display.

PGA - Pin Grid Array. An IC package that has multiple rows of pins on the bottom.

PIO - Programmed I/O. All devices support programmed I/O. The operating system executes IN and OUT instructions to read or write data one, two, or four bytes at a time to the device. There are four modes of PIO. PIO 1 (1 byte), PIO 2 (2 bytes), PIO 3 (3 bytes), and PIO 4 (4 bytes). The higher the PIO mode the faster the transfer time.

PLCC - Plastic Leaded-Chip Carrier. A popular chip-carrier package with J-Ieads around the perimeter of the package.

PLL - Phase Locked Loop. A circuit that synchronizes two clock signals often used in microprocessors to generate a 2x (or other integer multiple) frequency.

PnP - Plug and Play. A hardware and software specification developed by Intel that allows a PnP system and PnP adapter cards to automatically configure themselves. PnP cards are free from switches and jumpers and are configured via the PnP BIOS in the host system, or via supplied programs for non PnP systems.

A system intended to make fitting of expansion cards easier. In this context, ISA cards are known as Legacy Cards, and are switched as normal to make them fit in. Have as few of these as possible, as accesses to them are slow. With Concurrent PCI, the T II (or 430HX/VX) chip set's Multi Transaction Timer allows multiple transfers in one PCI request, by reducing re-arbitration when several PCI processes can take place at once. Passive Release allows the PCI bus to continue working when it's receiving data from ISA devices, which would normally hog the bus. Delayed Transaction allows PCI bus masters to work by delaying transmissions to ISA cards. Write merging combines byte, word and Dword cycles into a single write to memory.

The idea is that plug and play cards get interrogated by the system they are plugged into, and their requirements checked against those of the cards already in there. The BIOS will feed the data as required to the Operating System, typically Windows '95. Here you will be able to assign IRQs, etc to PCI slots and map PCI INT#s to them. Although Windows '95 or a PnP BIOS can do a lot by themselves, you really need the lot, e.g.a Plug and Play BIOS, with compatible devices and an Operating System for the best performance. Be aware that not all PCI (2.0) cards are PnP. PC (PCMCIA) cards are also "Plug and Play", but are not considered here.

PnP itself was originally devised by Compaq, Intel and Phoenix. chip set settings may allow you to choose of two methods of operation:

1. All PnP devices are configured and activated.

2. All PnP ISA cards are isolated and checked, but only those needed to boot the machine are activated. The ISA system cannot produce specific information about a card, so the BIOS has to isolate each one and give it a temporary handle so its requirements can be read. Resources can be allocated once all cards have been dealt with (recommended for Windows '95, as it can use the Registry and its own procedures to use the same information every time you boot).

POST - Power On Self Test. Instructions stored in ROM on the system mainboard which run only after the power is turned on. The most visible consequence of the POST is the memory test, where a number appears in the upper left corner of the screen and counts up until it reaches the total amount of memory (less the shadow area) installed on the machine.

PUN - Physical Unit Number. A term used to describe a device attached directly to the SCSI bus. Also known as a SCSI ID. As many as eight SCSI devices can be attached to a single SCSI bus, and each must have a unique PUN or ID assigned from 7 to 0. Normally the SCSI host adapter is assigned the highest-priority ID, which is 7. A bootable hard disk is assigned an ID of 6, and other nonbootable drives are assigned lower priorities.

PQFD - Plastic Quad Flat Pack. An IC package that has a single row of pins around all four sides.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Compiled by Scott McArdle, MagnaCom Limited. I hope this list has helped you and if there is an item that should be on this list, please let me know. Thanks. PS, I've spent 100's of hours maintaining this list, please don't be a LAMER.