Computer Science Topic 2

machine instruction cycle

basic operation cycle of a computer; the process by which a computer retrieves program instructions (fetch) from memory, determines what actions the instruction requires (decode), and carries out those actions (execute and optionally store).

CPU (Central Processing Unit)

Primary component of a computer that processes instructions; it runs the operating system and applications, constantly receiving input from the user or active software programs; it processes the data and produces output, which may be stored by an application or displayed on the screen.

ALU (Arithmetic Logic Unit)

An integrated circuit within a CPU that performs arithmetic and logic operations.

CU (Control Unit)

Part of the CPU that implements the microprocessor instruction set; it extracts instructions from memory and decodes and executes them, and sends the necessary signals to the ALU to perform the operation needed.

register

A small, very fast, temporary, memory storage location.

memory address register

A register on the CPU that either stores the memory address from which data will be fetched to the CPU or the address to which memory will be sent and stored.

memory data register

A register on the CPU that contains the data read from or to be stored in main memory.

primary memory

The primary memory of a computer is made up of the Read-Only Memory (ROM) and the Random Access Memory (RAM), CPU registers and Cache Memory. These are the memory or storage locations directly accessible to the processor.

secondary memory/storage

This is a non-volatile/persistent storage device used to store the operating system, applications and data in a computer system so that they are available the next time the system is started.

RAM (Random Access Memory)

Often referred to as Main Memory or simply Memory its the place in a computer where the operating system, application programs, and data in current use are kept so that they can be quickly reached by the computer's processor.

ROM (Read-Only Memory)

"Built-In" computer memory containing data that normally can only be read, not written to. It is accessed at start up and stores the Basic Input Output System (BIOS).

cache memory

Memory storage built on or very close to the CPU to allow super fast read/write access.

bus

A connection between two or more components of a computer system used for transporting binary information.

data bus

In a computer system it is used to transfer data to and from the CPU and Main Memory.

address bus

In a computer system this communicates the memory location to be read from/written to.

persistent storage (non-volatile)

A digital storage facility that doesn't lose its data after it loses its power supply e.g. magnetic hard disc, CD, DVD, Flash Memory

operating system

A collection of programs used to allow a computer system to be used. Consists of Input/Output (IO) control, File management, Software/hardware interface, Memory management, User interface, Scheduling, Program execution control and Security.

memory management

The process of controlling and coordinating computer memory, assigning portions called blocks to various running programs to optimize overall system performance.

Multitasking

allowing a user to perform more than one task at a time.

word processor

a computer program that provides special capabilities beyond that of a text editor such as the WordPad program that comes as part of Microsoft Windows operating systems.

Spreadsheet

a computer application that simulates a physical spreadsheet by capturing, displaying, and manipulating data arranged in rows and columns

database management system

a program that lets one or more computer users create and access data in a database

email

software which allows users to send and recieve electronic messages, attach files and forward on to others.

browser

an application program that provides a way to look at and interact with all the information on the World Wide Web

CAD (Computer-Aided Design)

software used by architects, engineers, drafters, artists, and others to create precision drawings or technical illustrations.

graphic processing software

software that allows the creation and manipulation of digital graphics e.g. photograph editing and manipulation

GUI

a graphical user interface to a computer. The design for common components such as toolbars, menus and dialogue boxes, are often provided by the operating system.

Toolbar

a horizontal row or vertical column of selectable image "buttons" that give the user a constantly visible reminder of and an easy way to select certain desktop or other application functions, such as saving or printing a document or moving pages forwards or backwards within a Web browser.

Menu

a set of options presented to the user of a computer application to help the user find information or execute a program function.

dialogue box

a small area on a screen, in which the user is prompted to provide information or select commands

Bit (binary digit)

the smallest unit of data in a computer (0 or 1).

Byte

a unit of data that is eight binary digits (bits) long; can represent a letter, number, or typographic symbol.

Binary

a numbering scheme in which there are only two possible values for each digit: 0 and 1.

denary/decimal

the base-10 number system, probably the most commonly used number system. (numbers 0-9)

hexadecimal

a base-16 number system.

data representation

the methods used internally to represent information stored in a computer.

Integers

a whole number that can be positive, negative, or zero.

Characters

a printable symbol having phonetic or pictographic meaning and usually forming part of a word of text, depicting a numeral, or expressing grammatical punctuation.

RGB

A way to digitally represent colours using binary numbers to represent varying levels of red (R), green (G) and blue (B) light. The more bits used for each, the more colours can be represented but taking up more storage.

Boolean operator

simple words (AND, OR, NOT, or AND NOT) used as conjunctions to combine or exclude keywords in a search, resulting in more focused and productive results

AND

the output is true when both inputs are true; otherwise the output is false.

OR

the output is true if either or both of the inputs are true; if both inputs are false then the output is false.

XOR

the output is true if either, but not both, of the inputs are true; the output is false if both inputs are false or if both inputs are true.

NOT

reverses the logic state.

NAND

operates as an AND gate followed by a NOT gate; the output is false if both inputs are true; otherwise the output is true.

NOR

operates as an OR gate followed by a NOT gate; output is true if both inputs are false; otherwise the output is false.

truth tables

a breakdown of a logic function by listing all possible values the function can attain.

logic gates

an elementary building block of a digital circuit.