GCSE AQA Computer Science - Definitions

Pregunta	Respuesta
Identifier	A unique name for something.
Constant	A named value within a program that is assigned a specific value.
Variable	An identifier associated with a particular memory location, used to store data.
Data type	A formal description of the type of data being stored in a variable. It defines the amount of memory required and the type of operations that can be performed on that variable.
Integer	Data type for whole numbers. Typically uses 2 or 4 bytes.
Boolean	True or False
Assignment	When a variable is a given a value.
Algorithm	A series of instructions that solves a problem in a finite number of steps and that always ends.
Pseudocode	A way of writing an algorithm that is close to actual programming language, using coding-style constructs such as IF...THEN...ELSE, loops and array notation as appropriate.
Logical operators	NOT, AND, OR. Used in conditions/Boolean expressions.
Sequence	Where instructions are executed one after another in series.
Selection	When the program will execute certain instructions based on conditions. Selection statements include: IF... THEN... ELSE and CASE... OF to select which commands to execute.
Iteration	Where a program will execute a group of instructions zero or more times based on a condition.
Procedure	A block of code that performs a specific task. It has an identifier by which it can be called from within the program.
Function	A block of code that always returns a single value.
Parameter	A variable whose value is being passed into a function or procedure
Global Variable	A variable that is declared in the main program and can be accessed anywhere in the program.
Local Variable	A variable that is declared within a function/procedure, so it can only be accessed within that function or procedure.
Syntax	A set of rules that defines how program statements must be written in order for the translator to understand them.
IDE	Integrated Development Environment. A programming environment that provides features such as: code editing, debugging help and run-time diagnostics.
Trace Tables	A manual way of tracking progress through an algorithm before it is coded. It tracks the changing values of variables through the code.
Database	A file of records.
API	Application Programming Interface. The interface provided by operating systems for programmers to create their own applications that run on it.
Open Source Programs	Programs that are shared free of charge by developers and can be used in other programs, as long as the resulting product is also Open Source.
Data Structures	Temporary structures in main memory that hold multiple data items while a program is running.
Array	A collection of data items with the same data type, which are grouped together under a single identifier.
Waterfall Model	A series of separate stages; each one is completed and provides inputs to the next.
Cyclical Model	Structured stages as in the Waterfall Model, but once the system is in maintenance stage it generates new problems that lead back into the feasibility and so on.
Spiral Model	Has several iterations of the stages. Successive passes through the stages produce a more refined prototype until the program is complete.
Erroneous Data	Data that is not the right type such as letters instead of numbers. Should be rejected.
MTBF	Mean Time Between Failure: A measure of availability often quoted by hardware manufacturers.
CPU	Central processing unit that contains the processor, main memory and cache.
Main Memory/RAM	Also known as Immediate Access Store and Primary Memory. The memory in the CPU that is used to temporarily store programs while they are running and data used by these programs.
Processor	The component in the computer that fetches, decodes and executes instructions.
Cache	High speed memory in the CPU that is used to store a copy of frequently used instructions and data.
Clock Speed	Measured in Hertz or cycles per second, it represents how many instructions per second the processor can execute.
System Buses	The circuits/internal wiring that connect the components within the CPU together.
RAM	Random Access Memory: a type of memory that is read-write and volatile. Used for Main Memory.
ROM	Read Only Memory: memory that is hard-coded at the time of manufacture. Stores the start up programs, the boot-strap loader.
Volatile	Describes memory that loses its contents when the power is switched off.
Non-Volatile	Describes memory that does not lose its contents when the power is switched off.
Virtual Memory	Part of the hard disk that is configured to behave as an extension to main memory.
EEPROM	Electronically Erasable Programmable Read Only Memory. A chip made up of a grid of transistors, each of which can be set to the value 1 or 0.
ASCII	American Standard Code for Information Interchange: A 7-bit character set used by PCs.
Pixel	Short for picture element. It is the smallest component of a bit-mapped image.
Metadata	Data about data. In the case of image files is the data the computer needs to interpret the image data in the file.
Analogue	A continuously changing wave such as natural sound.
Digital	Data that is made up of separate values. How data is stored on a computer.
ADC	Analogue to Digital Converter: Takes real-world analogue data and converts it to a binary representation that can be stored on a computer.
Data	Facts and figures with no context or format to give them meaning.
Information	Processed data that has context and format so that it conveys meaning.
LAN	A collection of computers and peripherals connected within a single site.
WAN	A collection of computers and LANs connected together over a geographically remote area, using leased infrastructure.
Peer-to-peer	A method of organising devices in a network where devices are all of equal status rather than having specialised roles.
Client-server	A method of organising devices in a network where some computers have specialised roles.
Protocol	A set of rules that defines how devices communicate.
Handshake	The communication between a client and server that initiates communication.
Record	Data stored about one instance of an entity.
Field	One specific data item being stored such as surname or show size.
Query	A feature of a database system that allows the database to be interrogated. It selects records from the database based on specified criteria.
Index	A mechanism for finding records in a file/database more quickly.

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