GCSE computer science

Fetch-execute Cycle

Instructions are fetched one by one from main memory decoded and then executed by the processor

CPU (Central Processing Unit)

A chip which controls the operation of all parts of the computer and executes program instructions

ALU (Arithmetic Logic Unit)

The part of the CPU responsible for arithmetic and logical operations

Processor Cache

High speed memory built into the CPU Instructions are copied for quicker access and increased speed

Register

A small area of memory within the CPU where data is stored temporarily

Von Neumann Architecture

The design defining registers the fetch-execute cycle and how the CPU interacts with main memory

MAR (Memory Address Register)

A register that holds the address of the instruction being read from or written to main memory

MDR (Memory Data Register)

A register that holds the instruction just copied from main memory

Program Counter

A register that holds the address of the next instruction to be fetched

Accumulator

A register that stores the result of the last operation

Clock Speed

How many instruction cycles the CPU can deal with in a second Measured in MHz or GHz

Cache Size

Larger cache means more instructions can be stored without transferring to main memory increasing performance

Cores

Each core contains its own ALU and registers capable of carrying out instructions independently

Embedded System

Specialist hardware and software built into a device with a single specific purpose

Primary Storage

Also known as memory Holds the data programs and instructions currently in use

RAM

Random Access Memory Stores running programs Data is lost when the computer is turned off

ROM

Read Only Memory Data cannot be changed and is not lost when the computer is turned off

Volatile Memory

Data stored in volatile memory is lost when the computer is turned off

Non-Volatile Memory

Data stored in non-volatile memory is not lost when the computer is turned off

Virtual Memory

Space on the hard drive used as main memory (RAM) Virtual memory is slower than main memory

Optical Storage

Secondary storage on a spinning disk Data is read or written using a laser

Magnetic Storage

Secondary storage which uses magnetic fields to store data

Solid State Storage

Secondary storage using flash memory They have no moving parts and are much faster

HDD (Hard Disk Drive)

Magnetic storage drive that stores large amounts of data Uses internal disks and a read/write head

SSD (Solid State Drive)

A solid state storage drive that performs the function of a traditional HDD

Bit

The smallest unit of storage containing a binary 1 or 0

Nibble

4 bits half a byte

Byte

8 bits

Kilobyte (KB)

1000 bytes

Megabyte (MB)

1000 KB

Gigabyte (GB)

1000MB

Terabyte (TB)

1000GB

Petabyte (PB)

1000TB

Binary

A number system used by computers containing only two symbols 0 and 1

Denary

The number system most often used by people It uses digits 0 to 9

Positive Number

A number greater than 0

Negative Number

A number less than 0

Integer

A whole number without a decimal point or fraction

Overflow Error

Happens when not enough space has been allocated to store the results of a calculation

Hexadecimal

A number system used by computers based on 16 symbols

Binary Shift

A process used to perform math on binary numbers by moving all the digits to the left or right

Most Significant Bit

The furthest left digit in a binary number its position means it has the highest value

Least Significant Bit

The furthest right digit in a binary number its position means it has the lowest value

Character

A single symbol for example a letter number or punctuation mark

Character Set

A system for representing characters in binary Each character is assigned a unique binary number

ASCII

American Standard Code for Information Interchange A 7 bit character set

Unicode

A much larger character set overcoming ASCII limitations It includes different language characters

Pixel

Short for Picture Element Pictures are divided into a grid where each square is one pixel

Metadata

Additional data about a file such as when it was created or who created it

Colour Depth

The amount of bits available for colours in an image Higher depth means more colours

Resolution

The number of pixels an image is divided into Higher resolution means clearer image

Sample Rate

The number of samples taken in one second Measured in hertz Hz

Bit Depth (Sound)

The number of bits available for each sample Higher bit depth means better quality

Analogue

A continuously varying signal usually represented as a curved line

Compression

A way of reducing the size of a file

Lossy Compression

Reduces file size by removing certain data The original file cannot be restored

Lossless Compression

Reduces file size without losing any data The original file can be restored

Network

Two or more computers connected together for sharing data or resources

LAN (Local Area Network)

A network which covers a small geographic area such as a single building

WAN (Wide Area Network)

A network which covers a large geographic area

Client - Server

A network where resources are centralized on a server and accessed by clients

Peer to Peer

A network where all computers have an equal status functioning as both client and server

Wireless Access Point

Uses a wireless radio to allow devices to connect wirelessly to an existing network

Router

A device which connects two or more different networks together allowing them to communicate

Switch

A device which provides computers and devices with a wired connection to a network

NIC (Network Interface Card)

A component allowing a device to connect to a network Controls sending and receiving data

Transmission Media

The physical connection which carries data between network devices

DNS (Domain Name System)

A system which links a URL or human readable name with an IP address

Hosting

The storing of files or other data on a server

The Cloud

Accessing storage or resources remotely across The Internet

Web Server

A server which hosts web sites and pages for users to access

Network Topology

The way computers and other network devices are connected together

Star Network

A network where all devices connect back to a single central point

Mesh Network

A network where all devices are connected to each other not a central point

Bandwidth

The amount of data which can be transferred via a network in any given time

The Internet

A global network connecting millions of computers and devices

URL

Uniform Resource Locator A human readable name given to websites

Client

A computer or device which accesses data from a central server

Ethernet

A physical copper cable used to connect devices on a network

Wi-Fi

A technology which uses wireless signals to connect network devices

Bluetooth

A short range wireless networking technology typically used for peripheral devices

Encryption

Converting data so it cannot be easily read or understood without first being decrypted

IP Address

Internet Protocol Address A unique address assigned to every computer on a network

IPv4

Internet Protocol Version 4 Addresses are four numbers separated by dots between 0 and 255

IPv6

Internet Protocol Version 6 Addresses are eight groups of hexadecimal characters

MAC Address

Media Access Control Address A 12 digit hexadecimal number assigned to a network interface card

Standard

An agreed way of doing something allowing products and services to work together

Protocol

An agreed set of rules for how network communications should take place

TCP/IP

Transfer Control Protocol / Internet Protocol A group of standards controlling how data is sent and received

HTTP

Hypertext Transfer Protocol A standard for transferring web pages between a client and web server

HTTPS

Hypertext Transfer Protocol Secure HTTP with security added Used for secure websites

FTP

File Transfer Protocol A standard for file transfer over networks

POP

Post Office Protocol A standard used by email clients to retrieve emails from an email server

IMAP

Internet Message Access Protocol A standard used by email clients to access emails stored on an email server

SMTP

Simple Message Transfer Protocol A standard used for the sending of emails over networks and The Internet

Malware

Software designed with malicious intent It may damage the computer monitor activity or delete data

Social Engineering

Gaining access to computer systems by targeting the people using the system

Phishing

Tricking someone into revealing information like passwords by pretending to be a trusted source

Brute-force attack

Attempting to guess a code or password by trying every possible solution

Denial of Service Attack

Attempting to send more traffic to a computer system than it can handle causing failure