Hardware Glossary

ACPI - Advanced configuration and power interface. The latest standard that specifies how PC or laptop power can be efficiently managed. Features include activating devices only when required and reducing clock speed when full processing power is not needed.

AGP - Accelerated graphics port. An expansion slot linked directley to the motherboard's system bus enabling high performance graphics. AGP graphics cards can access system memory directly, as well as using there own video memory. AGP 2x has a peak transfer rate of 512MBps (megabytes per second) while the AGP 4x runs at 1.1GBps (gigabytes per second).

ATAPI - The attachment packet interface is an extension to the EIDE interface spesification that additionally supports CD-ROM and tape drives.

Bios - Basic input/output system. Software stored in ROM (read-only memory) and used to start a PC when it is switched on. It checks that all required hardware components such as memory, disk drives and keyboard are present, loads key parts of the operating system and tells it what hardware is available.

bit - This is the smallest unit of data you can have, which has a value of 1 or 0 and is stored by a capacitor in a memory chip using different electrical currents. Addreviated b in data transfer rates, for example, 10kbps (10,000 bits per second).

Bluetooth - This is a specification for linking devices such as mobile phones, computers and PDAs (personal digital assistants) over a short-range wireless connection. The maximum range over which it can operate is currently 10 meters, with data transfer rates of up to 721kbps (kilobits per second).

bus master - An intelligent device such as a PCI adapter card that can gain control of the bus and use it to transfer data without involving the processor.

byte - A group of 8 bits used to represent a character or number with 4 bites representing a word. The binary system is used, so a kilobyte is 1.024 bytes while a megabyte is 1,048,576 bytes (noy 1,000,000 bytes). Abbreviated B in data transfer rates, for example 33MBps (33,000,000 bytes per second).

cache - A temporary storage area used to speed up different processes. A web browser keeps recently used web pages on a hard disk cache, so it doesn't have to download the same page again. A processor stores recent or frequently used instructions in small chunks of very fast memory called level 1 and 2 caches

CCD - A charge-coupled device that is used by digital and video cameras and scanners. It is a grid of light-sensitive cells that store an electrical charge proportional to the amount of light falling on them. The charge value in each cell is converted from analogue to digital and is used to build up a complete image.

Cmos - Complementary metal oxide semiconductor. A process used to make chips, but in a PC is shorthand for a battery powered chip on the motherboard which stores basic system configerations and clock settings.

CPU - Central processing unit. A microprocessor chip that is the 'brains' of a computer. It's many functions include fetching and carrying out instructions from programs.

Dimm - Duel inline memory module. A memory board that is effectively a double simm. It uses a 168-pin connector, and it's 64bit-wide bus allows single modules to be installed in Pentium systems

DRAM - The most common and cheapest form of computer memory which uses one capacitor and transistor to store one bit of information. It is 'volatile' memory, so if you turn off the power you will lose any stored data.

DVD - Digital versatile disk. A high-capacity CD-ROM disk that can store up to 17GB of data. The latest disks have two layers and DVD drives use a laser with two focal points to read each one. Each layer holds 4.7GB, so a duel-layer, duel-sided disk will store 17GB.

EPP/ECP - Enhanced parallel port/extended capabilities port. Improved parallel port which provides transfer rates of over 2MB (megabytes per second) and bidirectional operation. The latter is mainly used by printer monitoring software as it can receive status information from the printer while sending it data. ECP mode is designed for other devices such as Zip Drives.

EDO - Extended data out. To read a word of computer memory it must be precharged first. EDO memory speeds up this sequence by precharging the next word while still reading the current word.

enhanced IDE - An improved version of IDE that supports large hard disks, faster access speeds and DMA. It is actually two controllers providing primary and secondary channels, which handle two devices each, and can also talk to CD-ROM's and tape drives via Atapi.

FAT - File allocation table. A table that is held on a floppy or hard dist that tells the operating system the location of data and what order it is stored. Using 16bit addresses, it can only support disk sizes of 2MB whereas FAT32 uses 32bit addresses and supports hard disk sizes up to 2TB (terabytes).

FireWire - A very fast serial interface for connecting external devices. Also known as IEEE 1394 or iLink, it supports upto 63 devices and speeds of 400Mbps (megadytes per second). First implemented on the Apple Mac, it is more expencive than USB and suited more to devices that require high-speed transfer rates such as digital cameras.

IDE - Integrated drive electronics. Also known as ATA, this is the most common interface for connecting hard disks and other storage devices to a PC. As all the controller electronics are built into the device, it can be connected directley to the motherboard so you dont need a seperate adapter card (as you do with SCSI).

IRQ - Interrupt request signals are used by devices to, literally 'interrupt' the processor in order to gain it's attention. For example, every key pressed on a keyboard generates an interrupt signal indicating that an event has occurred that requires actiom. PCs support 15 hardware interrupts. Each device must have it's own IRQ or conflicts will occur that can cause a PC to hang or crash, although plug and play devices have alleviated this problem.

Midi - Musical instrument digital interface. The industry standard for connecting a musical instrament such as a keyboard to a PC.

parallel port - This is a 25-pin port on a PC that uses 8 wires to transfer one byte of data at a time at speeds up to 100KBps (kilobytes per second) and is used mainley for connecting printers.

PCI - Peripheral component interconnect. The most common bus design for motherboards and expansion slots.

Post - Power-on self test. The first process a PC runs when it is switched on which checks the memory, processor, graphics and so forth all are functioning. A series of beeps indicate if errors are found - One beep usually means that all is well.

Rimm - Rambus inline memory module. Also known as RDRAM, this memory has the potential to run at speeds upto 800MHz as opposed to SDRAM's max 133MHz. Speed is also increased by processing instructions 16bit at a time rather than 8bit.

SCSI - Small computer systems interface pronounced 'skuzzy'. An interface for connection hard disks and other compatable devices to a PC. More expensive than EIDE, but fast and more versatile, with the latest ultra 3 SCSI supporting upto 16 devices (including the SCSI adapter card or chip) and transfer rates of 160MBps (megabytes per second).

SDRAM - Synchronous DRAM. A type of memory that synchronises itself with the speed of the CPU's bus and can run at upto 133MHz. It's about twice as fast as EDO RAM and the latest SDRAM can run at 133MHz on PC's that support this speed.

Simm - Single inline memory module. A small board that holds a row of memory chips and has a 72-pin connector and uses a 32bit-wide bus. As Pentium processors have a 64bit bus, simms must be installed in pairs.

Smart - Self monitoring analysis and reporting technology. A feature of EIDE (on motherboards that support it) where the Bios can receive data about hard disk preformance and warn a user if it predicts a failure is likely to occur.

TFT - Thin film transistor. A high-quality liquid crystal display screen that uses between 1 and 4 transistors per pixel to control illumination. Each transistor requires little power and has a fast responce to changes as it can be switched on of off very quickley.

UDMA - Ultra DMA. The latest EIDE controllers that support transfer rates of 33MBps (megabytes per second), 66MBps and 100MBps - hence the terms UDMA33, UDMA66 and UDMA106.

USB - Universal serial bus. A plug and play interface on a PC allowing devices to be connected and used without and need for configuration by the user. USB supports up to 127 devices and speeds of 12MBps (megabytes per second) and allows devices to be removed or added without switching the PC off first.

VRAM - Video ram access memory. Special type of memory used for video adapters to speed up image display rates. Can be accessed simultaneously by two devices, so the digital to analogue converter (Ramdac) can provide screen updates while the video processor is supplying data.

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