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: a 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