Glossary of computer hardware terms

A

accelerator

a microprocessor, ASIC or expansion card designed to offload a specific task from the CPU, often containing fixed function hardware; a common example is a Graphics processing unit.

accumulator

a register in a CPU in which intermediate arithmetic and logic results are stored.

address

the unique integer number that specifies a memory location in an address space

address space

a mapping of logical addresses into physical memory or other memory mapped devices.

AI accelerator

an accelerator aimed running artificial neural networks or other machine learning and machine vision algorithms (either training or deployment), e.g. Movidius Myriad 2, TrueNorth, Tensor processing unit etc.

ATX

Advanced Technology extended - a motherboard form factor specification developed by Intel in 1995 to improve on previous DE factor standards like the AT form factor.

AT

The dimensions and layout (form factor) of the motherboard for the IBM AT.

AGP

Accelerated Graphics Port - a high-speed point-to-point channel for attaching a video card to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics.

B

bus

a subsystem that transfers data between computer components inside a computer or between computers.

Blu-ray Disc

an optical disc storage medium designed to supersede the DVD format.

C

cache

A small, fast local memory that transparently buffers access to a larger but slower or more distant/higher latency memory or storage device, organised into cache lines. Automatically translates accesses to the underlying resources address space to locations in the cache.

cache line

A small block of memory within a cache; the granularity of allocation,refills,eviction; typically 32-128 bytes in size.

cache coherency

The process of keeping data in multiple caches synchronised in a multi-processor shared memory system, also required when DMA modifies the underlying memory.

cache eviction

freeing up data from within a cache to make room for new cache entries to be allocated; controlled by a cache replacement policy. Caused by a cache miss whilst a cache is already full.

cache hit

finding data in a local cache, preventing the need to search for that resource in a more distant location (or to repeat a calculation).

cache miss

Not finding data in a local cache, requiring use of the cache policy to allocate and fill this data, and possibly performing evicting other data to make room.

cache thrashing

A pathological situation where access in a cache cause cyclical cache misses by evicting data that is needed in the near future.

cache ways

The number of potential cache lines in an associative cache that a specific physical addresses can be mapped to; higher values reduce potential collisions in allocation.

Card reader

a data input device that reads data from a card-shaped storage medium.

Computer case

the enclosure that contains most of the components of a computer (usually excluding the display, keyboard and mouse).

CD-R

Compact Disc-Recordable; a variation of the optical compact disc which may be written to once.

COMA

Cache-only memory architecture, a multiprocessor memory architecture where an address space is dynamically shifted between processor nodes based on demand.

Compact Disc-ReWritable

a variation of the optical compact disc which may be written to many times.

CD-ROM

(Compact Disc Read-Only Memory) - a pre-pressed optical compact disc which contains data or music playback.

chip

(or integrated circuit) - a miniaturised electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material.

control store

the memory that stores the microcode of a CPU.

core

the portion of a CPU which actually performs arithemetic and logical operations. A CPU may have multiple cores (e.g. "a quad-core processor").

core memory

in modern usage, a synonym for main memory, dating back from the pre-semiconductor-chip times when the dominant main memory technology was magnetic core memory.

CPU

Central processing unit - the portion of a computer system that executes the instructions of a computer program.

Conventional PCI

Conventional Peripheral Component Interconnect - a computer bus for attaching hardware devices in a computer.

Computer case

Computer chassis, cabinet, box, tower, enclosure, housing, system unit or simply case - the enclosure that contains most of the components of a computer (usually excluding the display, keyboard and mouse).

Computer form factor

The name used to denote the dimensions, power supply type, location of mounting holes, number of ports on the back panel, etc.

Chipset

(or chip set) - a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.

Channel I/O

a generic term that refers to a high-performance input/output (I/O) architecture that is implemented in various forms on a number of computer architectures, especially on mainframe computers.

D

data cache

D-cache

a cache in a CPU or GPU servicing data load and store requests, mirroring main memory (or VRAM for a GPU).

Computer data storage

a technology consisting of computer components and recording media used to retain digital data. It is a core function and fundamental component of computers.

Device memory

local memory associated with a hardware device such as a graphics processing unit or OpenCL compute device, distinct from main memory.

DASD

(Direct Access Storage Device) A mainframe terminology introduced by IBM denoting secondary storage with random access, typically (arrays of) hard disk drives.

DIMM

(dual in-line memory module);A series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers.

DisplayPort

DisplayPort is a digital display interface developed by the Video Electronics Standards Association (VESA). The interface is primarily used to connect a video source to a display device such as a computer monitor, though it can also be used to transmit audio, USB, and other forms of data.

Direct mapped cache

a cache where each physical address may only be mapped to one cache line, indexed using the low bits of the address. Simple but highly prone to allocation conflicts.

DMA

Direct memory access - the ability of a hardware device such as a disk drive or network interface to access main memory without intervention from the CPU, provided by one or more DMA channels in a system.

DVD

(Digital Video Disc or Digital Versatile Disc) - an optical compact disc - of the same dimensions as compact discs (CDs), but store more than six times as much data.

DVI

Digital Visual Interface (DVI) is a video display interface developed by the Digital Display Working Group (DDWG). The digital interface is used to connect a video source to a display device, such as a computer monitor.

Drive bay

DRAM

(Dynamic random-access memory) - a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit and which must be periodically refreshed to retain the stored data.

dual issue

refers to a superscalar pipeline capable of executing 2 instructions simultaneously.

E

Expansion card

a printed circuit board that can be inserted into an electrical connector, or expansion slot on a computer motherboard, backplane or riser card to add functionality to a computer system via the expansion bus. An expansion bus is a computer bus which moves information between the internal hardware of a computer system (including the CPU and RAM) and peripheral devices. It is a collection of wires and protocols that allows for the expansion of a computer.

F

Firewall

A hardware device or software to protect a computer from viruses, malware, trojans etc.

firmware

fixed programs and data that internally control various electronic devices.

floppy disk

a data storage medium that is composed of a disk of thin, flexible ("floppy") magnetic storage medium encased in a square or rectangular plastic shell.

floppy disk drive

a device for reading floppy disks.

Flash Memory

a type of non volatile computer storage chip that can be electrically erased and reprogrammed.

G

Graphics processing unit

H

hard drive

a non-volatile storage device that stores data on rapidly rotating rigid (i.e. hard) platters with magnetic surfaces.

hardware

the physical components of a computer.

HDMI

(High-Definition Multimedia Interface) - a compact interface for transferring encrypted uncompressed digital audio and video data to a device such as a computer monitor, video projector or digital television.

Harvard architecture

a memory architecture where program machine code and data are held in separate memories, more commonly seen in microcontrollers and digital signal processors.

I

input device

any peripheral equipment used to provide data and control signals to an information processing system.

input/output

the communication between an information processing system (such as a computer), and the outside world.

IOPS

(Input/Output Operations Per Second, pronounced eye-ops) - a common performance measurement used to benchmark computer storage devices like hard disk drives.

instruction

a group of several bits in a computer program that contains an operation code and usually one or more memory addresses.

instruction cache

I-cache

a cache in a CPU or GPU servicing instruction fetch requests for program code (or shaders for a GPU), possibly implementing modified Harvard architecture if program machine code is stored in the same address space and physical memory as data.

Instruction fetch

A stage in a pipeline that load the next instruction referred to by the program counter.

K

keyboard

an input device, partially modeled after the typewriter keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches.

L

Load/store instructions

instructions used to transfer data between memory and processor registers.

Load-store architecture

An instruction set architecture where arithmetic/logic instructions may only be performed between processor registers, relying on separate load/store instructions for all data transfers.

Local memory

memory associated closely with a processing element, e.g. a cache, scratchpad, the memory connected to one processor node in a NUMA or COMA system, or device memory (such as VRAM) in an accelerator.

M

mainframe

powerful computer used mainly by large organizations for bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.

main memory

the largest random access memory in a memory hierarchy (before offline storage) in a computer system; i.e. distinct from caches or scratchpads; usually consists of DRAM.

memory address

the address of a location in a memory or other address space.

memory architecture

Computer memory architecture

a memory architecture in a computer system, e.g. NUMA, uniform memory access, COMA, etc.

memory access pattern

The pattern with which software or some other system (an accelerator , or DMA channel) accesses memory, affecting locality of reference and parallelism.

Modified Harvard architecture

a variation of Harvard architecture used for most CPUs with separate non-coherent instruction and data caches (assuming that code is immutable), but still mirroring the same main memory address space, and possibly sharing higher levels of the same cache hierarchy

motherboard

the central printed circuit board (PCB) in many modern computers which holds many of the crucial components of the system, while providing connectors for other peripherals.

memory

devices that are used to store data or programs on a temporary or permanent basis for use in an electronic digital computer.

monitor

an electronic visual display for computers.

mouse

a pointing device that functions by detecting two-dimensional motion relative to its supporting surface; motion is usually mapped to a cursor in screen space; typically used to control a graphical user interface on a desktop computer or for CAD etc.

Mini-VGA

small connectors used on some laptops and other systems in place of the standard VGA connector.

Microcode

a layer of hardware-level instructions involved in the implementation of higher level machine code instructions in many computers and other processors.

Mask ROM

a type of read-only memory (ROM) whose contents are programmed by the integrated circuit manufacturer.

N

network

a collection of computers and other devices connected by communications channels, e.g. by ethernet or wireless networking

Network interface controller

also referred to as LAN card and network card.

NUMA

Non-uniform memory access

network on a chip

NOC

a computer network on a single semiconductor chip, connecting processing elements, fixed function units or even memories and caches. Increasingly common in System on a chip designs.

Non-volatile memory

memory that can retain the stored data even when not powered.

Non-volatile random-access memory

random-access memory that retains its data when power is turned off.

O

optical disc drive

a disk drive that uses laser light or electromagnetic waves near the light spectrum as part of the process of reading or writing data to or from optical discs.

Magneto-optical drive

Operating system

the set of software that manages computer hardware resources and provide common services for computer programs, typically loaded by the BIOS on booting.

Operation code

Several bits in a computer program instruction that specify which operation to perform.

P

pen drive

another name for a USB flash drive.

peripheral

a device attached to a computer but not part of it.

personal computer

Any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator.

prefetching

The pre-loading of instructions or data before needed either by dedicated cache control instructions or predictive hardware, to mitgate latency.

printer

A peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies.

Process node

refers to a level of semiconductor manufacturing technology, one of several successive transistor shrinks.

Processor node

a processor in a multiprocessor system or cluster, connected by dedicated communication channels or a network.

Processing element

an electronic circuit (either a microprocessor or an internal component of one) that may function autonomously or under external control, performing arithmetic and logic operations on data, possibly containing local memory, and possibly connected to other processing elements via a network, network on a chip, or cache hierarchy.

Prefetch (cache)

Prefetch

the process of pre-loading instructions or data into a cache ahead of time, either under manual control via prefetch instructions or automatically by a prefetch unit which may use runtime heuristics to predict the future memory access pattern.

PSU

Power supply unit - A unit of the computer that converts mains AC to low-voltage regulated DC for the power of all the computer components.

PROM

Programmable Read-Only Memory - a type of non-volatile memory chip that may be programmed after the device is constructed.

PCIe

Peripheral Component Interconnect Express - a computer expansion bus standard designed to replace the older PCI, PCI-X, and AGP bus standards.

PCI-X

PCI-eXtended - a computer bus and expansion card standard that enhances the 32-bit PCI Local Bus for higher bandwidth demanded by servers.

R

RAID

(Redundant Array of Independent Disks) - data storage schemes that can divide and replicate data across multiple hard disk drives in order to increase reliability, allow faster access, or both.

RAM

Random-access memory - any form of computer data storage that allow stored data to be accessed in any order (i.e., at random).

ROM

Read Only Memory - a type of memory chip that retains its data when its power supply is switched off.

S

server

a computer which may be used to provide services to clients.

software

computer programs and other kinds of information read and written by computers.

SIMM

Single in-line memory module - a type of memory module containing random access memory used in computers from the early 1980s to the late 1990s.

Solid-state drive

(or solid-state disk or electronic disk) a data storage device that uses integrated circuit assemblies as memory to store data persistently.

SRAM

Static random-access memory - a type of semiconductor memory that uses bistable latching circuitry to store each bit. The term static differentiates it from DRAM which must be periodically refreshed.

Sound card

an internal expansion card that facilitates economical input and output of audio signals to and from a computer under control of computer programs. It is also referred to as an audio card.

storage device

SDRAM

Synchronous dynamic random access memory - dynamic random access memory that is synchronized with the system bus.

SuperDisk

a high-speed, high-capacity alternative to the 90 mm (3.5 in), 1.44 MB floppy disk. The SuperDisk hardware was created by 3M's storage products group Imation in 1997.

T

tape drive

A peripheral storage device that allows only sequential access, typically using magnetic tape.

terminal

An electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system.

trackpad

Also known as a touchpad; a pointing device consisting of specialized surface that can translate the motion and position of a user's fingers or a stylus to a relative position on a screen.

TV tuner card

U

uop cache

a cache of decoded micro-operations in a CISC processor (e.g x86).

USB

Universal Serial Bus - a specification to establish communication between devices and a host controller (usually a personal computers).

USB flash drive

A flash memory device integrated with a USB interface. USB flash drives are typically removable and rewritable.

V

Video card

also referred to as a graphics card and several other names, a video card is an expansion card which generates a feed of output images to a display (such as a computer monitor).

VGA

Video Graphics Array - the last graphical standard introduced by IBM to which the majority of PC clone manufacturers conformed.

Volatile memory

memory that requires power to maintain the stored information.

W

Webcam

A video camera that feeds its images in real time to a computer or computer network, often via USB, Ethernet, or Wi-Fi.

Write back cache

A cache where store operations are buffered in cache lines, only reaching main memory when the entire cache line is evicted

Write through cache

A cache where store operations are immediately written to the underlying main memory.

Working set

The set of data used by a processor during a certain time interval, which should ideally fit into a CPU cache for optimum performance.