Computer Science Glossary

Looking for a quick answer? A definition or a very quick explanation of something? This is the right place to look, just make sure that you do know the background and extra information behind these ideas, concepts and terms.

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802.11b, g, n, ac - A set of international standards for the transmission of data using radio waves. Basically, the letter after 802.11 dictates how fast your wireless connection will be, with ac being the fastest and b being the slowest.

ALU - Arithmetic and Logic Unit - One of the most important components of a CPU, this is where any logical or mathematical instructions are carried out.

Backup - An exact copy of data which is stored externally from the original. Can be full or incremental. Remember, simply making a copy of a file does not make it a backup, it must be stored away from the system it was originally on.

Bandwidth - A measure of the amount of data that can travel through a cable/wireless connection in a given time frame. Usually measured in Mega Bits per second (Mbps)

Bit - The smallest quantity of storage in a computer system. A bit is either a 0 or a 1.

Blu-Ray - A type of optical storage used to hold software and video content. Typical capacity is 25 to 50Gb.

Byte - A collection of 8 bits. Can be used to represent any number up to 255 or 256 combinations of 0's and 1's.

Cat 5 (and 6) - A type of cable used to connect devices to a network. Sometimes called "ethernet" cable. Uses twisted pairs of copper cables to transmit data.

Capacity - A term used to describe how much data a device can store. Usually measured in Gigabytes or Terabytes.

CD - Compact Disc. A type of optical storage, usually used to hold music or software. Has a typical capacity of 700Mb.

Client - Server - A type of network where devices are connected to, and controlled by, one or more servers. Often seen as the "traditional" style of network.

Cloud Storage - Data that is stored on servers connected to the internet. Usually a rented/subscription service.

Coaxial - A type of cable used in networking. Usually found on "cable" internet services and TV services.

Computer - A machine which takes input in the form of binary, performs calculations, and processes instructions in the form of software in order to provide useful output.

Control Unit - Part of the CPU. Responsible for coordinating what the CPU is doing at each part of the FDE cycle.

CPU - Central Processing Unit - an internal component with a fixed instruction set. Carries out program instructions in a constant cycle called the Fetch-Decode-Execute cycle. CPU speeds are usually measured in Gigahertz (Ghz)

Device - A piece of hardware

DNS - Domain Name Server (or Domain Name Services) - A server which has the sole job of translating URL's (website addresses) into IP addresses. DNS servers are in a hierarchical structure and they are distributed across the Internet to spread the load on them.

DVD - A type of optical storage usually used to hold video or software data. Typical capacity of 4.7Gb. Stands for Digital Versatile (or sometimes video) Disc.

Execute - To carry out an instruction, to do as an instruction tells the CPU. Can also refer to the running of a whole program.

Fetch - Decode - Execute Cycle (FDE) - A cycle carried out by the CPU repeatedly until power is turned off. This involves the fetching of instructions or data from memory, decoding the instruction to work out what it means, followed by the executing (carrying out) of that instruction. 1 Cycle = 1Hz (hertz) and is the quantity by which CPU speed is measured.

Fibre Optic - A type of cable made from either plastic or glass which is used to transmit data in the form of light. The fastest type of cable, with the highest bandwidth.

Flash Memory - A special kind of memory chip which is non-volatile. Has lots of advantages over other types of storage such as its tiny size, low power consumption and fast read/write speeds.

Gigabyte - A measurement of storage, equivalent to 1024 Megabytes.

Gigahertz (Ghz) - A measure of CPU speed. 1Ghz = 1 Billion CPU cycles per second. The more Ghz, the more instructions a CPU can carry out per second.

Hard Disk Drive (HDD) - A method of mass storage in a computer. Hard drives are magnetic storage and use spinning discs called platters to hold data.

Hardware - The physical components of a computer system. To be hardware, you must be able to physically touch/hold it and it must form part of the computer system, for example RAM.

Hertz (Hz) - A measure of CPU speed. 1hz = 1 CPU cycle per second. The more hz, the more instructions a CPU can carry out per second.

Hub - A device which connects computers together on a network by simply broadcasting (copying) packets that are sent to every single device connected to the hub. These are no longer used as central points on networks. Note - anything advertised as a "home hub" or "super hub" from an internet provider is NOT actually a hub.

Input - Data going in to a computer system for the purpose of processing.

Input Device - A piece of hardware used to send data in to a computer system for processing.

Internet - A world wide network of networks. Not to be confused with the World Wide Web (WWW)

IP - Internet Protocol. Usually used alongside TCP. A stack which consists of rules that describe how data should be split into packets and how they will travel from one place to another.

IP Address - A 4 byte address, usually written in decimal (e.g. 192.168.1.1) given to a device on a network. This is used to ensure that devices can be identified on a network and traffic can be directed to the right place.

Kilobyte - A measurement of storage, equivalent to 1024 Bytes.

LAN - Local Area Network. A network confined to a small geographic area such as a house, office or school. Usually all equipment is dedicated to or owned by the organisation or person the network belongs to.

Magnetic Storage - Any method of storage based on magnetism or magnetic media, such as tape, floppy disks and hard disk drives.

Megabyte - A measurement of storage, equivalent to 1024 Kilobytes.

Megahertz (Mhz) - A measure of CPU speed. 1Mhz = 1 Million CPU cycles per second. The more Mhz, the more instructions a CPU can carry out per second.

Memory - An area of temporary storage (volatile) for open, running programs and data.

Memory Card - A type of small, portable, removable storage. Comes in two main types - SD (and micro SD) and CF. Uses flash memory technology.

Network - Two more more devices connected together for the purpose of sharing (data, resources) and communication.

NIC - Network Interface Card. This can be either wired or wireless and is simply the piece of hardware which allows a device to connect to a network.

Nybble - A collection of 4 bits. Can be used to represent numbers up to 15 or 16 combinations of 0's and 1's.

Optical Storage - A type of storage that uses a laser which is reflected off the surface of a disc to read data. Examples include CD, DVD and Blu-Ray.

Output - Data or information coming out of a computer system - the results of processing.

Output Device - A piece of hardware used to send out or display the results of processing

Packet - Data that has been broken into equal sized chunks to send across a network. A packet will contain some data, a source IP address, a destination IP address, some error correction or checksum data and a time to live counter (max number of hops before being discarded).

Peer to Peer - P2P - A type of network where all computers work collaboratively to share responsibility for managing the network, sending and receiving data and the sharing of resources such as processing power and storage. Often used in file sharing networks, for example Bit Torrent.

Platter - A metal disc inside a hard drive which is used to store data.

Processing - The carrying out of instructions, calculations or the manipulation of data in order to produce useful output.

Program - Another word for software or application. A list of instructions to be carried out by the CPU.

RAM - Random Access Memory. An area of temporary storage in a computer system, used to store currently open and running programs and data. Used to speed up system performance compared to fetching program data directly from storage. If RAM is filled then this can lead to much slower performance as the system has to resort to using virtual memory.

Register - a small piece of memory inside a CPU used to hold a single instruction or piece of data. Can also hold the result of processing an instruction in the CPU.

Router - A networking device that connects networks to other networks and routes packets between them. Routers will communicate with each other so they are able to forward packets not only to a destination network, but also closer to their destination - meaning a packet may travel through several routers before it arrives at its destination. Routers are responsible for making the internet work and for connecting LANs to WANs.

Secondary Storage - Usually refers to any type of non-volatile storage in a computer system

Software - The programs and features that run on a computer system. Software consists of a list of instructions that the CPU processes in order to "run" the program. Without software, a computer system would not do anything.

Solid State Storage - Any kind of storage which uses flash memory chips to hold data. This type of storage is non-volatile, consumes little power, is small and very quick to read and write data to.

Storage - A non-volatile device which holds programs and data. Can be internal or external. Examples are Hard Drives, SSD's, Memory Cards, USB Sticks and Optical Storage.

Switch - A central point on a LAN or in a star network topology. All devices on a LAN are usually connected to a switch, which then sends packets only to their intended destination. They can also be connected to routers to provide internet connectivity for a network.

Terabyte - A measurement of storage, equivalent to 1024 Gigabytes.

Traffic - A term used to discuss the volume of data being sent through a network. Very high levels of traffic (lots of packets) can result in poorer network performance.

Transmission Media - The method by which data is carried from one place to another on a network. This can be different types of wiring, such as ethernet cables, or it can be wireless methods such as WiFi.

USB - Universal Serial Bus. A standard for connecting a multitude of devices and peripherals to computers. Not to be confused with USB Memory Sticks.

USB Memory Stick - A convenient type of removable, portable, mass storage which connects to devices using the USB interface. Uses flash memory technology to store data.

URL - Uniform Resource Locator - Simply put, a website address.

Virtual Network or VLAN - When a physical network is divided or organised into several smaller "virtual" networks to help organise, secure and manage traffic on the network.

WAN - Wide Area Network. A network where computers are geographically remote from each other, or a network that covers a significant geographic area. WANs must make use of rented/leased telecommunications equipment such as internet connections.

WAP - Wireless Access Point. A piece of hardware on a network that allows devices to transmit and receive data wirelessly.

WWW - World Wide Web - A collection of information in the form of web pages that are linked together using hyperlinks. Not to be confused with the Internet!