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Computing Higher Computer Systems Glossary

Terms

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Firewall
A firewall is software or hardware which protects a local area network from outside access by monitoring and blocking network traffic.
Synchronous Transmission
The transmission of data between two devices is timed to a clock pulse
MPEG
A video data standard derived by the Motion Pictures Expert Group
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.
ROM based OS
An operating system program stored on a ROM chip.
News Server
A News Server is a computer which stores and forwards Usenet messages.
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.
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
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.
Data compression
A technique of reducing the storage space occupied by a file
Instruction Register
Used to hold the current instruction that is being executed
Cycle Time
The cycle time is the time between clock pulses.
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.
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
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
ADC
Analogue to digital converter used to generate a digital signal from analogue input
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
Pixel
A picture element which is the smallest display element
Network Topology
The arrangement of computers to form a network
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
Keyboard Controller
A special integrated circuit that is used to receive and interpret keyboard scan codes
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).
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.
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.
Accuracy
A measure of how well a computer representation of an image, sound etc. matches the original
Pixel Replication
The replication of pixels in the x and y direction by a scale factor to produce an enlarged image
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
EEPROM
Electrically Erasable Programmable Read Only Memory can be selectively reprogrammed
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
Memory Upgrade
Expanding physical memory by adding more RAM modules.
CCD
Charge-Coupled Device used to record light intensity. CCDs form the heart of scanners and digital cameras
Vector Graphic
A mathematical representation of a graphical object
HTML
Hypertext Markup Language
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".
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
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
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.
Stored Program
A series of machine instructions that are held in main memory
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.
Ring Network
Each device is connected on the network to a ring communications line around which signals are sent
Network
A network is one or more computers connected together in a way which allows them to communicate or share data and resources.
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.
Inter-block Gap
Used to describe the empty space between data blocks on a tape device
Hypermedia
When data elements are linked to form a structure through which the user can navigate
Bubble Jet Printer
Operates by heating the ink until it forms a vapourised bubble which is then squirted as a tiny droplet of ink onto a page
Sampling
An analogue sound value measured every nth fraction of a second and stored digitally
Asynchronous Transmission
A character is sent as soon as it is available rather than using a clock pulse to synchronise transfer
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.
Network Operating System
An operating system that that manages access to data and resources on a network, ensuring the privacy and security of data.
Character Printer
A device which prints characters one at a time. Examples include the daisy wheel or golf ball
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
Character Set
The set of characters that can be represented and displayed by a computer
SRAM
Static Random Access Memory. Very fast volatile store suited to cache memory
QuickTime
An Apple standard for storing and playing video data. Provides a methodology for interleaving audio data with video data.
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".
Client/Server
A network model where data is held and controlled centrally on a file server and accessed by individuals on a workstation
Arithmetic Logic Unit
The heart of a computer where data is processed and manipulated
Bandwidth
Bandwidth describes the amount of data which can be transmitted via a network connection, usually measured in bits per second.
UNIX
UNIX is a network operating system originally developed by AT Bell laboratories.
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.
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
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.
Multiscan Monitor
Display technology able to deal with different scanning frequencies
Track
A circular section of a disk that is divided into equal-length sections called sectors
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.
ASCII
American Standard Code for Information Interchange
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
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.
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.
Binary number system
A system in which numbers are represented using only the digits 0 and 1.
LINUX
LINUX is an open source operating system developed by Linus Torvalds.
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.
Bus Network
Each device on the network is directly connected to a single communications line
Adjustable-Split Keyboard
A three-piece folding keyboard organised into three adjustable sections
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.
IR
The Instruction Register, IR, is a register in the CPU. It holds the instruction currently being executed.
System bus
The medium for communicating data and control signals between the main components of the computer.
Unicode
A 16-bit symbol representation system
Adware
Adware is software which is free to use but which pays for itself by presenting the user with advertising material.
Internetwork
An internetwork is two or more computer networks connected together.
Interface
A unit that sits between the CPU and a peripheral device and compensates for the differences in speed, codes, etc
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.
Boot Program
A small program held in ROM that is executed when the computer is powered up
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
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.
Stop Bit
Marks the ends of a character in asynchronous transmission
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.
Capacity
The amount of data that can be stored
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.
Redirector
A redirector is a LAN device driver which translates operating system requests into network events and transmits them to the right protocol stack.
Bit map
A representation of image data where each bit corresponds to an individual pixel on the screen
Sample Size
The amount of data that is stored per sample
Interactive Multimedia
Multimedia presentation where the end user can control what is being displayed by activating buttons and hyperlinks on a page
Raster Graphics
A method of producing an image on a display screen by illuminating horizontal lines of dots on the screen
Customised Keypad
A specially designed input device that can be programmed
Parallel Transmission
Each bit of an 8-bit byte is transmitted along a set of parallel wires at the same time
Address Bus
Used to pinpoint a memory location
CU
The Control Unit, CU, is part of the CPU. It exerts overall control over the operation of the CPU.
Spam
Spam is a term used to describe electronic junk mail.
Resolution
The total number of pixels in the width and height of an image
Pit
Pits are areas burned on a CD-ROM by a laser - typically 0.5 microns wide and 0.83 to 3 microns long
Flop
Floating point operations per second
Token
A signal that passes around a network and is a carrier for a data packet
Network Manager
Person who controls access to services and shared resources on a local area network.
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.
MIPS
MIPS stands for Millions of Instructions Per Second. This is used as a performance measure.
Control Characters
Special non-printing characters in a character set, used for special purposes, e.g. carriage return and end of file
Rotational Speed
The speed at which a disk rotates. Measured in revolutions per minute (rpms)
Direct Access
Referred to as random access. The retrieval of any disk data given the sector location
Curie Temperature
The point at which magnetic material ceases to be a permanent magnet
Wide Area Networks
A network linking machines worldwide
Video Controller
Special circuitry that is used to generate the signals needed for a video output device to display data
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.
Cache Memory
A small amount of random access memory that sits between the processor and RAM in order to speed up data transfer
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.
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
Scan Code
A code that is generated when a key is pressed on the keyboard
Mantissa
A non-zero value used to represent the precision of a decimal number
Internal bus
The medium for communicating data and control signals between the component parts of the CPU.
MAR
The MAR, or Memory Address Register, specifies the address in memory for the next read or write operation from or to memory.
Quantisation
The rounding of sound samples to the nearest integer
Collision
A collision occurs when two devices transmit simultaneously on an Ethernet network.
Virtual Memory
Part of the hard disk is used as if it was main memory.
UART
Universal Asynchronous Receiver/Transmitter
File Server
Provides centralised storage and resource management for users of a network
Non-Volatile
A characteristic of a memory chip which keeps its contents when power is removed
Byte
Eight units of binary data (bits).
Browser
Software used to render HTML pages
Email Clients
an email client is a piece of software which can be used to connect to an email server and retrieve electronic mail.
Ethernet
A popular local area network commonly using coaxial cable with transmission rates of 10 or 100Mbps
Avi
Audio Video Interleaved
Repetitive Strain Injury
A disorder that is caused by awkward posture or movement when using a keyboard
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.
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
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.
URL
Uniform Resource Locator
Data encryption
A method of securing transmitted data through encoding
Exponent
Represents the range of a decimal number
Start Bit
Marks the beginning of a character in asynchronous transmission
Bit
A single unit of binary data.
SCSI
Small Computer Systems Interface
Sampling Rate
The number of sound samples that are taken per second
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.
Program Counter
An internal register of the CPU used to hold the address of the next instruction to be executed
Machine Cycle Time
The cycle time for one fetch-execute-cycle, sometimes expressed in MIPS, millions of instructions per second
Tele-working
Tele-Working is the ability to work from somewhere geographically separate from the company you work for.
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.
DRAM
Dynamic Random Access Memory. Slower, volatile store that needs to have a continuous signal to refresh the contents of the chip
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
Volatile
Refers to a type of memory which loses its contents when power is no longer supplied to the chip
Video Digitising
The conversion of analogue video data to a digital represenatation
Clipping
Reducing the amplitude of a sound sample to fall within a given sample range
Flat-bed Scanner
An input device similar to a photocopy machine where documents are scanned, face down on a glass surface
Matrix Printer
A device which forms characters or graphics out of ink dots
Bit-depth
The number of bits used to represent each pixel.
Modified Keyboard
Keyboards that have been redesigned to suit the needs of the workplace or to improve the health and safety of users
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)
Sign and Magnitude
The most sigificant bit of the word is used to represent the sign of the number with the remaining bits representing the magnitude
Serial Transmission
Each bit of the byte is sent out, one at a time over the communications line
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
Removable Storage
A storage device that is external to the computer and can be disconnected to facilitate data transfer to another machine
Windows 2000 Server
Windows 2000 Server is a network operating system developed by Microsoft as a replacement for Windows NT.
Bi-Directional
Transfers data in both directions
VRAM
A separate memory, operating at high-speed used to hold screen data that is to be displayed
Disk Based OS
An operating system that is distributed on and loaded from disk
Coercivity
A property of magnetic storage devices which describes how easily magnetization can be switched from one orientation to another
ALU
The Arithmetic and Logic Unit, ALU, is part of the CPU. It carries out computation.
Metropolitan Area Networks
A network which interconnects buildings or other facilities extending over a citywide area
Cylinder
A collection of tracks on each platter that are equidistant from the spindle
Uni-Directional
Transfers data in one direction only
Integrated Keyboard and Touchpad
A keyboard containing both keys and a touchpad
Skewing
Occurs in parallel transmission where the individual bits of a byte arrive may at their destination at different times
Process
A program in execution.
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.
Windows NT
Windows New Technology (NT) is a network operating system developed by Microsoft.
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
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.
Resolution Independent
A graphical representation that is independent of the display resolution
Star Network
All devices on the network connect though a central connection point or controller
Accumulator
A special purpose register used by the Arithmetic Logic Unit to hold the accumulated results of calculations
Boolean
Two-state algebra developed by George Boole.
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.

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