PC Glossary

AGP

Accelerated Graphics Port. An evolution of PCI, optimised for adding graphics cards to a PC system. Uses a 32 bit wide bus, clocked at 66 MHz. So-called AGP 1x devices transfer one 32 bit word each clock period, whilst AGP 2x devices can transfer a 32 bit word on both the rising and falling edges of the clock. The former gives a data rate of 267 Mbytes/s, the latter 533 Mbytes/s.

AT

A standard motherboard shape, occasionally referred to as a form factor, which also defines case shapes. Usually used as a modifier ("AT motherboard", "AT case"). Now being superseded by the ATX and NLX standards.

ATX

A relatively new motherboard shape, intended to replace the AT standard. Like AT, the shape of the motherboard also determines the layout of the case. See also NLX.

Celeron

Intel's supposedly low-end range of processors, although their performance differs little from the higher-priced Pentium 2. The Celeron is available for clock speeds of 266, 300, 333, 366 and 400 MHz, in both Slot 1 and Socket 370 packages. There are two types of Celeron core, one without Level 2 cache, the other with 128 kbytes of Level 2. The former core was used in the 266 and 300 MHz models, the latter in all subsequent units. Note that there are two types of 300 MHz Celeron: the "300" has no Level 2 cache, the "300A" has 128 kbytes.

EIDE

Enhanced Integrated Drive Electronics. A step beyond IDE, offering two 'channels' for a total of four devices.

Firewire

(aka IEEE 1394) A high-speed serial interface, originally intended for connecting digital video devices. Currently specified in 100 Mbit/s, 200 Mbit/s and 400 Mbit/s data rate versions. Future versions may support 800 Mbit/s and 1.6 Gbit/s. Proposed by some as a replacement for current interfaces such as SCSI.

IDE

Integrated Drive Electronics. The standard hard disc interface in PCs and more recent Acorn machines. Allows the connection of two devices, mainly hard discs and CD-ROMs, to the computer.

IEEE 1284

A specification for an advanced form of parallel or printer port. It defines an 8 bit, bi-directional parallel interface with better support for general data transfer tasks.

ISA

Industry Standard Adaptor. The old standard PC expansion bus, 16 bits wide and clocked at 8 MHz. Most systems still have a few ISA slots provided, although it has now been superseded by PCI.

Level 1 Cache

A small block of fast memory close to a processor's core. Keeps a temporary store of data recently read from or written to main memory, with the aim of minimising slow memory accesses. Level 1 cache is closest to the processor, and is always checked first. It is usually integrated on the silicon die with the processor core. See also Level 2 Cache

Level 2 Cache

Similar to Level 1 Cache, but at one further remove from the processor. Level 2 cache is checked if the data required is not in the Level 1. It is usually made up of a larger amount of slightly slower memory. Level 2 cache used to be a feature of the motherboard, but it is increasingly being moved closer to the processor. The Alpha has its Level 2 integrated on the die, like the Level 1, and Intel has moved this way with the Celeron. The Pentium 2 and Xeon use separate Level 2 cache chips, packaged on a module with the processor.

Merced

The first processor to use Intel's new architecture, dubbed IA-64. Due for launch in 2001, unless it has slipped again. This one is a 64 bit design, aimed at the top end of the market and likely to have a price tag to match. Merced will be followed by McKinley.

NLX

A new motherboard shape, targeted at the lower end of the PC market. Notable for its separate PCI and ISA slot daughterboard, into which the motherboard plugs. Once again, cases must be designed to accept this arrangement. See also the contemporary ATX and the earlier AT.

PCI

Peripheral Component Interconnect. The standard PC expansion bus, supplanting the ISA interface. Comprises a 32 bit wide bus, clocked at 33 MHz. A 64 bit PCI standard exists, but few systems support it.

PCMCIA

Personal Computer Memory Card Interface Adaptor. A credit-card sized expansion for laptops. Also referred to as PC Cards. PCMCIA devices include hard discs, modems, and mobile phones.

Pentium

Intel's successor to the 80486 processor. Widely described as a 64 bit device; in reality, only its memory bus is 64bits wide. Ancestor of both the Pentium Pro and Pentium 2.

Pentium 2

Intel's current range of more expensive processors. Originally produced for clock speeds of 233, 266, 300, 333, 350, 400 and 450 MHz. Only the last three are still in production. The Pentium 2 name actually covers a range of processor designs; these are usually referred to by their internal Intel code-names.

Pentium 3

The recently-announced name for the next Intel processor, expected towards the end of March '99. This device will use the Katmai core, be packaged in the SECC2, and will initially be available at clock speeds of 450 and 500 MHz.

Pentium Pro

A development of the Pentium processor, intended for workstation and server use. Notable for the Level 2 cache chip placed in the ceramic package with the processor. Rumour has it that Intel never achieved a satisfactory production yield on this device, leading to the development of the Pentium 2 and the withdrawal of the Pro from sale.

SCSI

Small Computer Systems Interface. A general-purpose expansion bus, commonly used for the connection of hard drives, CD-ROMs, tape drives and scanners to computers. The main competitor to EIDE. Comes in many variations, SCSI-1, SCSI-2 and SCSI-3. The latter is also called UltraSCSI.

SDRAM

Synchronous Dynamic Random Access Memory. A form of main memory; basically, standard DRAM (as has been used since the days of the BBC) with a clocked interface. Specified by the maximum clock speed it can use, for example 66 MHz or 100 MHz.

SECC

Single Edge Connector Cartridge. Intel's package for the Pentium 2 processor range, a separate PCB with plastic cover and heatsink attachments which contains the processor itself and the Level 2 cache devices. The design has recently been simplified to produce the SECC2.

SGRAM

Synchronous Graphics Random Access Memory. A clocked version of Video RAM. As SDRAM is to DRAM, so SGRAM is to VRAM. It has two data in/out ports, allowing both the graphics chip and the processor to access the memory at the same time.

Slot 1

Intel's mechanical and electrical specification for attaching a Pentium 2 processor module to a motherboard. Note that the Celeron range are not designed for Slot 1, although the mechanical differences are minor. See also Slot 2, Slot M and Slot A.

Slot 2

Intel's mechanical and electrical specification for attaching a Pentium 3 processor module to a motherboard. See also Slot 1, Slot M and Slot A.

Slot A

Nothing to do with Intel, this one. An open standard proposed by AMD and Digital / Compaq, for attaching a processor module to a motherboard. Modules using DEC Alpha and AMD K7 processors are currently planned for this interface. Notable for specifying the Digital EV6 memory bus, which is capable of a maximum clock speed of 200 MHz. See also Slot 1, Slot 2 and Slot M.

Slot M

Intel's mechanical and electrical specification for attaching a Merced processor module to a motherboard. See also Slot 1, Slot 2 and Slot A.

Socket 7

A processor socket specification, employed by Intel's Pentium, AMD's K6, and Cyrix' M2 amongst others. See also Socket 370, and the various Slot types.

Socket 370

Intel's new socket specification for the Celeron processor, replacing the current Slot design. Intended to reduce the manufacturing cost of the Celeron.

SVGA

Super Video Graphics Adaptor. An enhanced VGA, usually referring to a resolution of 800 by 600 pixels.

UltraDMA

A high-speed data transfer protocol for EIDE interfaces. DMA stands for Direct Memory Access, indicating that the interface can transfer directly between disc and memory, without using the processor.

USB

Universal Serial Bus. A general purpose serial interface, intended for connecting a wide range of common peripherals. Current uses include mice, keyboards, speakers and digital cameras. Uses a data rate of 10 Mbit/s, and provides power to connected devices. Also features hot-swapping, allowing devices to be connected or removed whilst the rest of the system is switched on.

UltraSCSI

Also known as SCSI-3, the latest version of the SCSI system. There's also an Ultra2SCSI!

VGA

Video Graphics Adaptor. An early PC video standard, usually referring to a resolution of 640 by 480 pixels. Occasionally used, loosely, to refer to PC's graphics system in general. See also SVGA and XGA.

Windows 95

Microsoft's replacement for Windows 3.1.

Windows 98

An upgrade to Windows 95, from Microsoft.

Windows 2000

The proposed name for Microsoft's next operating system update. Was to be Windows NT 5.

Windows CE

Microsoft's palm-top operating system, designed to look like Windows 95 whilst requiring less processing power and memory.

Windows NT

Microsoft's "serious" operating system, intended as a competitor to UNIX.

x86

A generic term used to refer to processors compatible with Intel's 8086 range. As well as Intel's products (8086, 80186, 80286, 80386, 80486, Pentium, Pentium Pro, Pentium 2), it can also refer to Cyrix (5x86, 6x86, M2) and AMD (K5, K6).

Xeon

A slightly up-rated Pentium 2, at a much inflated price. The Xeon is available at clock speeds of 400 and 450 MHz, and with Level 2 cache sizes of 512 kbytes, 1Mbytes and 2 Mbytes. Unlike the Pentium 2, the cache runs at the same speed as the processor core.

XGA

The next step up from SVGA, usually referring to a resolution of 1024 by 768 pixels.

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