GCSE Computer Science (OCR)

Arithmetic Logic Unit (ALU)

Performs operations on data e.g. Addition, subtraction

Control Unit (CU)

Coordinating activities of the CPU

Registers

Quick, small stores of data within the CPU

Memory Address Register (MAR)

Holds memory address for data or a instruction about to be used by the CPU

Memory Data Register (MDR)

Holds actual data or instruction

Accumulator

Stores results of calculations in the ALU

Program Counter (PC)

Holds memory address of the instruction for each cycle

Fetch

The next instruction is retrieved by CPU from main memory

Decode

The instruction is broken down and decided so computer can understand

Execute

The CPU performs what the instructions told

Embedded System

A computer system built within a large device e.g. Camera, washer, car

Volatile

Memory loses its data when power off

Non-volatile

Memory retains its data when power is lost

Random Access Memory (RAM)

Read/write - function is to load open programs and operating system data currently in use - volatile

Read Only Memory (ROM)

Can only be read, can't be changed, stores essential programs to be run in order to boot the computer - non-volatile

Cache

A type memory that stores copies of frequently used data, much faster than RAM, lower capacity - closer to CPU

Buses

Collection of wires that carry signals between various components of the computer system

Central Processing Unit (CPU)

Processes all of the data and instructions that make the system work - can be effected by clock speed, number of cores, cache size

Clock speed

How fast the computer does the FDE cycle

virtual memory

A memory management procedure needed when the RAM is full so a temporary section is made which acts like a part of RAM

Flash memory

Solid state storage, non-volatile, more reliable/durable but can only be overwritten a limited number of times

Graphics Processing Unit (GPU)

Handles graphics and image processing

Optical storage

CD, DVD, Blue-ray
ADV: cheap,easy to transport
DIS: slow, less storage than hard drives, stored data degrades over time, cannot be written over

Magnetic storage

Hard drives
ADV: fast access, stores large amounts of data, low cost
DIS: not very portable, easily be broken

Solid State storage

USB, flash memory, SD
ADV: fast, small, light, easily potable, quiet
DIS: more expensive, storage capacity less, limited number erase/write cycles

Cloud stotage

Data is stored on multiple servers in a remote location
ADV: secure, can be accessed anywhere, no need to buy
DIS: needs internet, download and upload can be effected by internet connection, less control if data is held

Operating System

essential software that links the hardware and other software together and generally manages the computer system

Command-line Interface

Text commands where user has to type in command

Graphical User Interface (GUI)

uses icons and other visual indicators to navigate and issue commands

Utility Software

maintains a computer

Defragmentation Software

reorganises data on the hard drive to put fragmented files back together and moves files to collect all the free space

Backup Software

Full Backup - a copy is taken from from every file on the system
Incremental Backup - only files created or edited since last backup are copied

Compression Software

reduces file size so they take up less space on hard disk

Encryption Software

scrambles data to stop others from accessing it

Open Source Software

source code is made freely available and users can modify it
ADV: free, ,made for greater good, can be adapted
DIS: small, buggy, security holes, no warranties, no customer support

Proprietary Software

only the compiled code is released and the source code is kept a secret
ADV: warranties, well-tested, reliable, cheaper
DIS: expensive, software may not fit user needs

analogue signal

a continuous signal which can't be processed by a computer

ALU

part of CPU that carries out arithmetic and Boolean operations

ASCII

A 7-bit character set consisting of 128 characters

assembly language

low-level langauge

authentication

a process for checking user identity

binary

a counting system using base-2 consisting of 0s and 1s

binary shift

moving the bits in a binary number left or right and filling gaps with 0s

BIOS

Basic Input Output System

bitmap image

a graphic made up of pixels

bit

a binary digit either 0 or 1