Computing Paper 1 OCR

Arithmetic Logic Unit (ALU)

Carries out all arithmetic calculations and logical decisions

Control Unit (CU)

coordinating all activities around CPU

Registers

Quick, small stores of data within the CPU

Memory Address Register (MAR)

Holds address of memory location for data to be fetched from or sent to

Memory Data Register (MDR)

Stores data to be fetched from memory or to be sent to memory

Accumulator

Stores results of calculations in the ALU

Program Counter (PC)

Holds address of next instruction instruction to be processed

Fetch( Relating to registers)

Address of next instruction copied from PC placed in MAR, now containing a memory address

CU fetches that data copying to MDR

PC incremented to next instruction to be processed

Decode(Relating to registers)

MDR contains either data fetched from memory/instruction. CU decoding it to see what to do next

Execute( Relating to registers)

May include using ALU, locating data in memory, changing pc value etc

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 requiring power

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, doesn’t require power to maintain content

Cache

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

Central Processing Unit (CPU)

Processes all of the data and instructions that make the system work

Clock speed

Number of cycles per second

virtual memory

Uses part of hard drive as extra RAM

Helps when you don’t have enough RAM

Moving less-used data from RAM to hard drive freeing RAM

When data is needed again it is moved back to 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

Using lasers to read data

CD, DVD, Blue-ray

Advantages, disadvantages of optical

ADV: cheap, easy to transport

DIS: slow, less storage than hard drives, stored data degrades over time, cannot be written over

Magnetic storage

Rotating magnetic disks with a read/write head moves across surface

Hard drives

Advantages and disadvantages of magnetic

ADV: fast access, stores large amounts of data, low cost

DIS: not very portable, easily be broken, Higher power requirements

Solid State storage

Flash memory

USB, flash memory, SD

Advantages and disadvantages of Solid state

ADV: fast, small, light, robust, quiet, No moving parts, low power requirements

DIS: more expensive, storage capacity less, limited number erase/write cycles

Cloud stotage

Data is stored on multiple servers in a remote location

Advantages and disadvantages of cloud storage

DIS: needs internet, download and upload can be effected by internet connection, less control if data is held

ADV: secure, can be accessed anywhere, no need to buy

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

Software that helps configure and analyse performance to ensure it’s running effectively

Defragmentation Software

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

Compression Software

reduces file size so they take up less space in storage

Encryption Software

converts data into a coded format 

cannot be understood when intercepted

Uses algorithm and key to convert plaintext into cyphertext and viceversa

Open Source Software

source code is made freely available and users can modify it

Advantages and disadvantages of open source

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

Advantages and disadvantages of proprietary software

ADV: warranties, well-tested, reliable, cheaper

DIS: expensive, software may not fit user needs

Local Area Network (LAN)

a network that connects devices close to each other e.g. school, house

Wide Area Network (WAN)

a network within a large geographical area e.g. internet

Bandwidth

amount of data that can be transferred in a given time

Network Interface Card (NIC)

component allow a device to connect to a network

Switch

Allows data to be passed between devices in network

Router

responsible for transmitting data between networks

Ethernet

Protocol for connecting devices on wired WAN

Client-server Network

client has connection to server and request resources, servers can backup and store centrally but can be expensive and difficult to maintain

Peer-to-peer Network

no central server, each computer equal in responsibility, have to work as both server and a client.

Star Topology

ADV: better performance, rest of network not affected in one fails, simple to add more devices

DIS: wire needed for all devices, expensive

Mesh Topology

ADV: faster

DIS: expensive

MAC Address

assigned to all devices, unique to all devises and cannot be changed, permanent, identifies the actual device.48 bits/6 groups of 2 hexadecimal digits

e.g. 1A:5B:6C:98:78:35

IP Address

assigned either manually or automatic, the location of your device on the internet

Packet Switching

split data into packets to be sent across the network, each packet given a number order of data, each router reads packet header and decides which way to send it according to IP rules, packets then arrive and reassemble them in the right order.

TCP/IP

sets of rules for how devices connect on the network.

Hyper Text Transfer Protocol (HTTP)

used to access websites and communicate with web servers

HTTPS

more secure - encryption

File Transfer Protocol (FTP)

used to access, edit and move files between devices

Post Office Protocol (POP3)

used to retrieve emails from a server, holds until download - then deletes from server

Internet Message Access (IMAP)

used to retrieve emails, server holds until you actually delete it- only download a copy

Simple Mail Transfer Protocol (SMTP)

used to send emails, used to transfer emails between servers

Layer advantages

ADV: manageable pieces, self-contained can change without effecting others

Domain Name Server (DNS)

translates websites' domain name into its IP address

Phishing

used to gain personal information for purposes of identity theft, using fraudulent e-mail messages that appear to come from legitimate businesses.

Shouldering

used to obtain information such as personal identification numbers (PINs), passwords and other confidential data by looking over the victim's shoulder.

Malware

malicious software - computer programs designed to infiltrate and damage computers without the users consent.

Virus

program loaded onto a user's computer without the user's knowledge and performs malicious actions. It can self-replicate, inserting itself onto other programs or files, infecting them in the process.

Worm

program that replicates itself in order to spread to other computers. Often, it uses a computer network to spread itself, relying on security failures on the target computer to access it.

Trojan Horse

program which misleads users of its true intent.

Brute Force Attack

trail and error to gain information

Denial of Service Attack (DOS)

hacker stop users from accessing a part of a network, flooding network with useless traffic making computer very slow

Data Interception And Theft

The unauthorized taking or interception of computer-based information. Data theft is the act of stealing computer-based information from an unknowing victim with the intent of compromising privacy or obtaining confidential information.

SQL Injection

programming language used to search and query databases.

Penetration Testing

organisations employ specialists to stimulate potential attacks on their network

Anti-malware Software

designed to find and stop malware from damaging a network

Encryption

data is translated into code which only someone with the correct key can access

Data Protection Act

Data must be processed lawfully/fairly

Used for declared purposes only

secure

not kept longer than necessary

Computer Misuse Act

Cannot have unauthorised access with intent to

commit further offences

intent to modify computer material

Copyright Act

protect intellectual property

Cannot give copy to friend

No selling

No renting without permission

Advantages and disadvantages of more clock speed

ADV: Faster the clock speed more instructions can be completed per second

DIS: If CPU can’t keep up data can be corrupted. can overheat

Number of cores

Can process instructions simutaneously splitting work among cores 

Can only work with software that was designed to be used with multiple cores

Primary Storage

Storage for data CPU needs to access quickly

Secondary storage

Non-volatile storage

ASCII

7 bit code representing alphabet, numbers, some symbols

Unicode

16 bit code which can represent many characters with wide range of symbols

Pixels

Smallest element of an image

Stored as binary code

How to find colours that can be stored in a pixel

2 to the power of bits

Resolution

Amount of pixels per unit of measurement

Higher colour depth

better looking image

larger file size

Higher resolution

Made larger without losing resolution

Fetch

Instruction in the form of data retrieved from main memory

Decode

Instruction converted to readable format

Execute

CPU performs action according to instruction

Von Neumann Architecture

Data and instructions stored in the same memory

Examples of metadata

Image resolution

colour depth

Image width

Image height

File type

Date created

Sample rate

Why we use binary

Computers use switches which can only be either on/off

Binary can represent on/off using digits 1/0

Why is hexadecimal used

Preferred when working with large values

Shorthand binary calculations

Takes fewer digits to represent values than in binary

Helpful as more bits harder to read, prone to errors

Overflow error

Occurs when number becomes to large to store the number of bits available

Text file size formula

Number of characters*bits per character

Image file size formula

Colour depth*Image height*Image width