GLOSSARY – COMPUTER SYSTEMS
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| Term | Description |
| Accumulator | A special purpose register used by the Arithmetic Logic Unit to hold the accumulated results of calculations |
| Accuracy | A measure of how well a computer representation of an image, sound etc. matches the original |
| ADC | Analogue to digital converter used to generate a digital signal from analogue input |
| Address Bus | Used to pinpoint a memory location |
| Adjustable-Split Keyboard | A three-piece folding keyboard organised into three adjustable sections |
| ADSL | ADSL stands for Asymmetric Digital Subscriber Line – a modem technology which converts existing twisted-pair telephone lines into access paths for multimedia and high-speed data communications. ADSL can transmit up to 6Mbps to a subscriber, and as much as 832Kbps or more in both directions. |
| Adware | Adware is software which is free to use but which pays for itself by presenting the user with advertising material. |
| ALU | The Arithmetic and Logic Unit, ALU, is part of the CPU. It carries out computation. |
| Arithmetic Logic Unit | The heart of a computer where data is processed and manipulated |
| ASCII | American Standard Code for Information Interchange |
| Asynchronous Transmission | A character is sent as soon as it is available rather than using a clock pulse to synchronise transfer |
| Avi | Audio Video Interleaved |
| Bandwidth | Bandwidth describes the amount of data which can be transmitted via a network connection, usually measured in bits per second. |
| Bi-Directional | Transfers data in both directions |
| Binary number system | A system in which numbers are represented using only the digits 0 and 1. |
| Bit | A single unit of binary data. |
| Bit-depth | The number of bits used to represent each pixel. |
| Bit map | A representation of image data where each bit corresponds to an individual pixel on the screen |
| Bluetooth | Bluetooth is a wireless networking protocol which allows devices to connect together to provide services like Internet access, printing and data transfer without the intervention of the user. |
| Boolean | Two-state algebra developed by George Boole. |
| Boot Program | A small program held in ROM that is executed when the computer is powered up |
| Broadcasting | Broadcasting over a network uses the User Datagram Protocol which does not require an acknowledgment. This is a more efficient use of bandwidth than individual downloads. |
| Browser | Software used to render HTML pages |
| Bubble Jet Printer | Operates by heating the ink until it forms a vaporised bubble which is thensquirted as a tiny droplet of ink onto a page |
| Buffer | A part of memory used to hold data when communicating with a peripheral. Used when a fast acting part of the system (CPU) is exchanging data with a slow acting device (printer) |
| Bus Network | Each device on the network is directly connected to a single communications line |
| Byte | Eight units of binary data (bits). |
| Cache Memory | A small amount of random access memory that sits between the processor and RAM in order to speed up data transfer |
| Caching | A cache is a local copy of data available over a network. When for example a web page is requested, the network software retrieves the page, but also saves it locally. When the page is requested again, it will make it available from the cache, thus speeding up the process of viewing the page. This only works for web pages which do not have dynamic data on them or which have not altered recently. The system works better for graphics and other elements of a web page which do not change very often. |
| Capacity | The amount of data that can be stored |
| CCD | Charge-Coupled Device used to record light intensity. CCDs form the heart of scanners and digital cameras |
| Central Processing Unit | The (CPU) coordinates and controls the activities of all other units in the computer system. It executes program instructions and manipulates data in accordance with the instructions |
| Character Printer | A device which prints characters one at a time. Examples include the daisy wheel or golf ball |
| Character Set | The set of characters that can be represented and displayed by a computer |
| Chatrooms | Chatrooms are areas on the Internet where users can communicate using text messages in real time. Chat servers can be accessed using an IRC client which allows you to select different discussion areas which you can join or leave. |
| Client/Server | A network model where data is held and controlled centrally on a file server and accessed by individuals on a workstation |
| Clipping | Reducing the amplitude of a sound sample to fall within a given sample range |
| Coercivity | A property of magnetic storage devices which describes how easily magnetization can be switched from one orientation to another |
| Collision | A collision occurs when two devices transmit simultaneously on an Ethernet network. |
| Control Characters | Special non-printing characters in a character set, used for special purposes, e.g. carriage return and end of file |
| Control Unit | Includes timing/control logic and an instruction decoder. It sends signals to other parts of the computer to direct the fetch and execution of machine instructions |
| CPU | The CPU, or Central Processing Unit. This is where instructions are processed and computations are carried out. This is the control centre of the computer. |
| CU | The Control Unit, CU, is part of the CPU. It exerts overall control over the operation of the CPU. |
| Curie Temperature | The point at which magnetic material ceases to be a permanent magnet |
| Customised Keypad | A specially designed input device that can be programmed |
| Cycle Time | The cycle time is the time between clock pulses. |
| Cylinder | A collection of tracks on each platter that are equidistant from the spindle |
| Data Bus | Used to transfer data to and from the CPU. The data bus can be common to devices and main memory allowing transfers to take place from and to peripherals or from and to main memory |
| Data compression | A technique of reducing the storage space occupied by a file |
| Data encryption | A method of securing transmitted data through encoding |
| Data Overrun | This occurs when the CPU ignores an interrupt request from a peripheral. The interface merely discards the byte and informs the CPU that data has been lost |
| Direct Access | Referred to as random access. The retrieval of any disk data given the sector location |
| Disk Based OS | An operating system that is distributed on and loaded from disk |
| DRAM | Dynamic Random Access Memory. Slower, volatile store that needs to have a continuous signal to refresh the contents of the chip |
| EEPROM | Electrically Erasable Programmable Read Only Memory can be selectively reprogrammed |
| Electronic Forum | An electronic forum is a web based discussion area which require users to join before they can post a message or query. They are often used by software distributors to provide technical support and feedback for their products. |
| Email is system of communication which allows users on a network to send text messages and attached files to another user. Email addresses are usually of the form: username@domainname. | |
| Email Clients | an email client is a piece of software which can be used to connect to anemail server and retrieve electronic mail. |
| EPROM | Electrically Programmable Read Only Memory can have the contents erased and replaced with new data by the user. Data is erased by shining ultraviolet light onto the chip |
| Ethernet | A popular local area network commonly using coaxial cable withtransmission rates of 10 or 100Mbps |
| Exponent | Represents the range of a decimal number |
| External Memory | Holds quantities of data too large to store in main memory. It is also used to keep a permanent copy of programs and data |
| Fetch-Execute Cycle | The repeated process of fetching instructions from main memory, decoding the instructions and executing them until an instruction to HALT is encountered |
| File Server | Provides centralised storage and resource management for users of a network |
| File servers | A file server is a dedicated machine on a network which controls access to resources on a network. A file server will usually be running a network operating system and have enough disk space to give every user on the network space to store files. |
| Firewall | A firewall is software or hardware which protects a local area network from outside access by monitoring and blocking network traffic. |
| Flat-bed Scanner | An input device similar to a photocopy machine where documents are scanned, face down on a glass surface |
| Flop | Floating point operations per second |
| Freeware | Freeware is software which is distributed free by the programmer, or is a cut down version of a commercial product which is distributed free in the hope that users will purchase the full version. |
| General Purpose Package | An application package that provides more than a single type of application to solve specific problemse.g. word processing, database, spreadsheet, etc |
| General Purpose Registers | A set of registers internal to the CPU whose role is not defined at the time of manufacture. Programmers may use these registers as appropriate within their programs |
| HTML | Hypertext Markup Language |
| Hub | A hub is a multi-port repeater in an Ethernet network. Hubs are used to distribute a network connection to a number of machines in a room or an area of a building. Hubs typically have 12 or 24 ports. |
| Hypermedia | When data elements are linked to form a structure through which the user can navigate |
| Instruction Register | Used to hold the current instruction that is being executed |
| Integrated Keyboard and Touchpad | A keyboard containing both keys and a touchpad |
| Interactive Multimedia | Multimedia presentation where the end user can control what is being displayed by activating buttons and hyperlinks on a page |
| Inter-block Gap | Used to describe the empty space between data blocks on a tape device |
| Interface | A unit that sits between the CPU and a peripheral device and compensates for the differences in speed, codes, etc |
| Internal bus | The medium for communicating data and control signals between the component parts of the CPU. |
| Internet | The Internet is a global internetwork consisting or millions of computers connected together using a variety of high speed communications systems. Home users connect to the Internet using the telephone system. |
| Internetwork | An internetwork is two or more computer networks connected together. |
| Intranet | An intranet is a private network which provides similar services within an organisation to those provided by the Internet outside it but which is not necessarily connected to the Internet. An intranet is often used for distribution of information within the organisation. Some organisations give limited access to their intranets to other organisations or the general public. This is known as an “extranet”. |
| IR | The Instruction Register, IR, is a register in the CPU. It holds the instruction currently being executed. |
| ISDN | ISDN stands for Integrated Services Digital Network. With ISDN, voice and data are carried by bearer channels (B channels) occupying a bandwidth of 64 Kbps (Kilo-bits per second). Some switches limit B channels to a capacity of 56Kbps. A data channel (D channel) handles signaling at 16 Kbps or 64 Kbps, depending on the service type. |
| Keyboard Controller | A special integrated circuit that is used to receive and interpret keyboard scan codes |
| LINUX | LINUX is an open source operating system developed by Linus Torvalds. |
| List-Server | A list-server is an email based electronic conference. Any message sent to the list server will be automatically emailed to everyone on that list. |
| Local Area Network | A Local Area Network (LAN) is a number of computers connected together within a single building or organisation. Local area networks tend to be characterised by high bandwidth, low error rates and short distances between computers. |
| Logic gates | A device that performs a logical operation upon its input signals to produce its output signals. |
| Machine Code Program | A binary code program that is executable by a specific computer processor |
| Machine Cycle Time | The cycle time for one fetch-execute-cycle, sometimes expressed in MIPS, millions of instructions per second |
| Main Memory | (RAM) stores programs and data while the computer is operating. It is organized so that data can be both read from and written to it. It is a volatile store that loses its contents when the machine is switched off |
| Mantissa | A non-zero value used to represent the precision of a decimal number |
| MAR | The MAR, or Memory Address Register, specifies the address in memory for the next read or write operation from or to memory. |
| Matrix Printer | A device which forms characters or graphics out of ink dots |
| MDR | The MDR, or Memory Data Register, contains the data to be written to memory or receives the data read from memory. The MDR is sometimes known as the Memory Buffer Register (MBR). |
| Memory Address Register | An internal register of the CPU that is used to hold the address of a location in main memory |
| Memory Buffer Register | Used to hold data that has just been sent to or from the CPU |
| Memory Upgrade | Expanding physical memory by adding more RAM modules. |
| Metropolitan Area Networks | A network which interconnects buildings or other facilities extending over a citywide area |
| MIPS | MIPS stands for Millions of Instructions Per Second. This is used as a performance measure. |
| Modified Keyboard | Keyboards that have been redesigned to suit the needs of the workplace or to improve the health and safety of users |
| MPEG | A video data standard derived by the Motion Pictures Expert Group |
| Multiscan Monitor | Display technology able to deal with different scanning frequencies |
| Multi-tasking | Where several applications are open at the same time, and the user can switch easily between them. |
| NetBEUI | NetBIOS Extended User Interface (NetBEUI) is a network protocol developed by Microsoft and originally used with LAN Manager. |
| Network | A network is one or more computers connected together in a way which allows them to communicate or share data and resources. |
| Network Interface Card | A Network Interface Card (NIC) is an interface fitted inside a personal computer or network terminal which allows it to communicate with other machines over a network. The card technology will vary according to the network used, but every card on a network must have some way of uniquely identifying itself and some means of converting the signals form the computer to a form which can be transmitted over the connection. |
| Network Manager | Person who controls access to services and shared resources on a local area network. |
| Network Operating System | An operating system that that manages access to data and resources on a network, ensuring the privacy and security of data. |
| Network Topology | The arrangement of computers to form a network |
| Newsgroups | Newsgroups are electronic bulletin boards for text based discussion on any subject. Un-moderated newsgroups allow any user to post a message. Moderated newsgroups have an administrator who filters messages before they are posted. |
| News Server | A News Server is a computer which stores and forwards Usenet messages. |
| Non-Volatile | A characteristic of a memory chip which keeps its contents when power is removed |
| Page Printer | A device which generates an entire page image. The data is sent to the printer as an entire page which requires it to have a fairly large internal memory. Example include the laser printer. |
| Parallel Transmission | Each bit of an 8-bit byte is transmitted along a set of parallel wires at the same time |
| Parity Bit | An additional bit that is transmitted as part of a byte. The parity bit is altered to reflect even or odd parity. Data transmitted can be checked using the parity bit to ensure there are no errors during transmission |
| PC | The Program Counter, PC, is a register in the CPU. It holds the address in memory of the next instruction to be executed in the program. |
| Peer to Peer | A network model where all computers on the network are equal and data may be shared from computer to computer. Any node may set itself up as a file server |
| Pit | Pits are areas burned on a CD-ROM by a laser – typically 0.5 microns wide and 0.83 to 3 microns long |
| Pixel | A picture element which is the smallest display element |
| Pixel Replication | The replication of pixels in the x and y direction by a scale factor to produce an enlarged image |
| Process | A program in execution. |
| Program Counter | An internal register of the CPU used to hold the address of the next instruction to be executed |
| Proxy Server | A Proxy Server is a machine which receives requests for internet pages and forwards them. A proxy server can provide a LAN with a single point of access to the Internet and can act as a filter to block access to unsuitable material. |
| Quantisation | The rounding of sound samples to the nearest integer |
| QuickTime | An Apple standard for storing and playing video data. Provides a methodology for interleaving audio data with video data. |
| RAID | A Redundant Array of Inexpensive hard Disks (RAID) is a method of providing fault tolerant hard disk storage so that if one disk fails, the operating system can recover the data from the other disks and recreate the failed hard disk image when it is replaced. |
| Raster Graphics | A method of producing an image on a display screen by illuminating horizontal lines of dots on the screen |
| Redirector | A redirector is a LAN device driver which translates operating system requests into network events and transmits them to the right protocol stack. |
| Removable Storage | A storage device that is external to the computer and can be disconnected to facilitate data transfer to another machine |
| Repetitive Strain Injury | A disorder that is caused by awkward posture or movement when using a keyboard |
| Resolution | The total number of pixels in the width and height of an image |
| Resolution Independent | A graphical representation that is independent of the display resolution |
| Ring Network | Each device is connected on the network to a ring communications line around which signals are sent |
| ROM based OS | An operating system program stored on a ROM chip. |
| Rotational Speed | The speed at which a disk rotates. Measured in revolutions per minute (rpms) |
| Router | A router is a computer with two network cards which is responsible for routing data from one network to another. A router keeps track of the IP addresses of the computers on the networks connected to its network interface cards and directs IP packets appropriately. A router functions at the Network layer of the OSI model. |
| Sample Size | The amount of data that is stored per sample |
| Sampling | An analogue sound value measured every nth fraction of a second and stored digitally |
| Sampling Rate | The number of sound samples that are taken per second |
| Scan Code | A code that is generated when a key is pressed on the keyboard |
| SCSI | Small Computer Systems Interface |
| Search Engine | A search engine is a service provided on the Internet which indexes web pages. When you enter a term in a search engine it will respond with a list of all the web pages it has indexed where that term occurs. Using a search engine takes practice as it is important to choose the term you search for with care so that the search engine returns a usable number of “hits”. |
| Sector | A simplified representation of data storage is to view the surface of the disk as having 1s, representing a “north” magnetisation and 0s, representing a “south” magnetisation. Strictly speaking, the data is compressed using run-length limited (RLL) encoding, but this method and its purpose are beyond the scope of this topic. The smallest addressable portion of a track and the smallest unit of data that can be read or written |
| Serial Transmission | Each bit of the byte is sent out, one at a time over the communications line |
| Shareware | Shareware is software which requires you to pay a fee to the distributor if you want to continue using it after a certain period of time. Sometimes the trial period is enforced by the software ceasing to function after the period has expired, sometimes the decision is left to the user’s conscience. |
| SHTTP | Secure Hyper Text Transmission Protocol (SHTTP) encrypts data transmitted over the Internet. It is often used to allow users to purchase items over the Internet using e-commerce, or to transfer sensitive information. |
| Sign and Magnitude | The most significant bit of the word is used to represent the sign of thenumber with the remaining bits representing the magnitude |
| Skewing | Occurs in parallel transmission where the individual bits of a byte arrive may at their destination at different times |
| Spam | Spam is a term used to describe electronic junk mail. |
| Spooling | The temporary storage of input or output data on magnetic disk or tape. Preferred method used when a peripheral is shared across a network or when large data files are being transferred |
| SRAM | Static Random Access Memory. Very fast volatile store suited to cache memory |
| Star Network | All devices on the network connect though a central connection point or controller |
| Start Bit | Marks the beginning of a character in asynchronous transmission |
| Stop Bit | Marks the ends of a character in asynchronous transmission |
| Stored Program | A series of machine instructions that are held in main memory |
| Stored program concept | The idea that the sequence of instructions to solve a problem should be stored in the same memory as the data. This concept was proposed by John Von Neumann in 1945. |
| Switch | A switch is a device to divide an Ethernet network up into separate collision domains. A switch keeps a database of the address of each machine on the network and only transmits a frame of data for a machine on to the segment of cable which that machine is connected to. |
| Synchronous Transmission | The transmission of data between two devices is timed to a clock pulse |
| System bus | The medium for communicating data and control signals between the main components of the computer. |
| Tele-working | Tele-Working is the ability to work from somewhere geographically separate from the company you work for. |
| Token | A signal that passes around a network and is a carrier for a data packet |
| Track | A circular section of a disk that is divided into equal-length sections called sectors |
| Two’s Complement | A representation of negative integers that is formed by changing each 1 bit to a 0 and each 0 bit to a 1 and then adding 1 |
| Two-State Machine | Electronic components of a computer that can be in one of only two states. Binary digits 0 and 1 are used to represent these two states |
| UART | Universal Asynchronous Receiver/Transmitter |
| Unicode | A 16-bit symbol representation system |
| Uni-Directional | Transfers data in one direction only |
| UNIX | UNIX is a network operating system originally developed by AT Bell laboratories. |
| URL | Uniform Resource Locator |
| UTP | Unshielded Twisted Pair (UTP) cabling is used in 10baseT and 100baseT Ethernet installations. It consists of thin cables twisted together to avoid interference created by electrical induction. UTP cabling is classified according to the data transfer rate it can support and its immunity to interference. |
| Vector Graphic | A mathematical representation of a graphical object |
| Video Conferencing | Video Conferencing is a system using video cameras, and a high bandwidth network connection such as an ISDN line which allows a number of people to communicate with each other using sound, video and to share data such as text and graphics even though they are thousands of miles apart. |
| Video Controller | Special circuitry that is used to generate the signals needed for a video output device to display data |
| Video Digitising | The conversion of analogue video data to a digital representation |
| Virtual Memory | Part of the hard disk is used as if it was main memory. |
| Volatile | Refers to a type of memory which loses its contents when power is no longer supplied to the chip |
| Von Neumann architecture | Von Neumann architecture is based upon the basic idea that the sequence of instructions to solve a problem should be stored in the same memory as the data. |
| VRAM | A separate memory, operating at high-speed used to hold screen data that is to be displayed |
| Web Server | A web Server is a piece of software running on a machine on a network which provides which sends out web pages in response to requests from Internet browsers. |
| Wide Area Network | A Wide Area Network (WAN) is a number of computers connected together which are geographically remote. Wide are networks tend to be characterised by low bandwidth, high error rates and long distances between computers. A wide are network may not be controlled by any one organisation. |
| Wide Area Networks | A network linking machines worldwide |
| Windows 2000 Server | Windows 2000 Server is a network operating system developed by Microsoft as a replacement for Windows NT. |
| Windows NT | Windows New Technology (NT) is a network operating system developed by Microsoft. |
| Wireless Application Protocol | Wireless Application Protocol (WAP) is a protocol which runs on mobile phones and provides a universal open standard for bringing Internet content to mobile phones and other wireless devices. |
