A-level Computing 2009/AQA/Print version/Unit 2/Definitions


 * Boolean variable: has two discrete values: true or false
 * Truth Table: a table that shows the results of applying a logical operation
 * Boolean equation: an equation that expresses a boolean output in terms of boolean inputs and the functions applied
 * Logic gate: an electronic circuit that performs a boolean function
 * Hardware: Electronic circuits that a computer is assembled from/ The platform on which software executes
 * Main memory: Memory that is directly accessible to the processor
 * Memory location: a separately addressable area of main memory
 * RAM: random access memory; volatile memory in which the locations can be accessed directly in any order
 * ROM: read only memory; non-volatile memory that cannot be written to after it has been set up
 * EEPROM: electrically erasable programmable read only memory; read only memory which's contents may be altered
 * Computer Bus: a set of parallel wires connecting independent components of a computer
 * System Bus: the main set of buses connecting the processor, main memory and I/O controllers, consisting of the data, control and address bus
 * Peripheral:a computer device that is not part of the central processing unit
 * I/O device:a hardware unit that sends or receives data or stores data, by communicating with the processor via a I/O controller
 * I/O controller:an electronic circuit that connects to a system bus and an I/O device
 * Secondary storage:permanent data storage not directly connected to the processor
 * Memory address:an unique numeric code corresponding to a location in memory
 * Stored program concept:a program must be present in main memory to be executed; it is processed by fetching machine code instructions in sequence from the main memory and executing these codes, one at a time in the processor
 * Register:a very fast memory location inside the processor or I/O controller
 * General purpose registers:a register that is not assigned a specific role
 * Dedicated registers:a register assigned a specific role by the processor designer, e.g. the MBR or MAR
 * Clock speed:the frequency in megahertz at which the processor executes instructions
 * Word length:the number of digits in a binary word, e.g. 8-bits
 * Bus width:the number of wires in a bus
 * Machine code instruction:a binary code that a machine can understand
 * Compiled high level language program:a program translated into machine code before it is executed on a computer
 * Op-code:the part of a machine code instruction that denotes the basic machine operation, e.g. ADD
 * Operand:the part of a machine code instruction that represents a single item of data used by the op-code
 * Instruction set:the set of bit patterns or binary codes for the machine operations that a processor has been designed to perform
 * Track:one of the concentric rings on a platter of a hard disk
 * Sector:a subdivision of a track
 * Disk block:the smallest unit of transfer between a computer and a disk; the size of a sector (size as in binary length)
 * USB:Universal Serial Bus; allows peripherals to be connected using a standard interface socket
 * Access time:the time the time between accesses on a storage device
 * Software:a series of instructions that are executed by the hardware
 * Assembler:translates assembly code into machine code
 * Compiler:translates high level language code into object code
 * Interpreter:analyses and executes high level language code line by line
 * Bespoke software:written for a customer's specific need
 * General purpose software:software that can be used for many different tasks
 * Special-purpose software:software designed to support a specific task
 * Internet:a network of computer networks and computers using unique IP addresses and communicate via the TCP/IP protocols
 * Gateway:connects networks that use different link layer protocols
 * Router:connects networks that use the same link layer protocol
 * IP-Address:a unique address that identifies a computer or other device on a network
 * WWW:World wide web; a system of interlinked hypertext documents accessed via the internet
 * Domain name:a name that identifies one or more IP addresses
 * FQDN:Fully Qualified Domain Name; it consists of a host ID and domain name
 * DNS server:server that translates fully qualified domain names into IP addresses
 * URL:Uniform Resource Locator; a URI that identifies a resource by its network location
 * URI:Uniform Resource identifier; specifies how to access a resource on the internet
 * Server:a software process that provides a service requested by a client
 * Client:a software process that requests and uses the services provided by a server
 * Client-Server model:a client software process initiates a request for a server software process to respond to