CS Revision - Computer Systems & Data Representation

Flashcards covering weaknesses I have at these OCR GCSE Computer Science (Higher) topics

6 Functions of an OS

Communication with hardware

Provide a UI

Provide a platform to run applications

Allow computer to multitasking

File/disk management

User management

OS - Communication

Uses device driver software to translate signals for hardware to the OS. Installs drivers when a new device is connected

OS - UI

Allows a user to interact with a computer system

Can be GUI, CLI, or mobile UI

Advantage/Disadvantage of CLI

More efficient and powerful than GUI

Not usable for everyday users

WIMP

Windows Icons Menus Pointers

OS - Multitasking

Removes unused applications from memory

Uses a memory manager to allocate applications certain memory addresses

Divides CPU time and may prioritise some applications

OS - File/Disk management

Organises data into a heirarchial structure

Splits hardware into sectors

May include utility software

OS - User management

Lets each user have only access to their own data

May use security measures

Account system

Difference between single user and multi user OS

Multi user OS allows several users to use a computer at the same time. Often used on mainframes

Embedded systems

Computers built into other larger devices

Used to monitor and control machinery

Dedicated to perform a single task

Advantages of embedded systems

Cheaper to produce and more efficient at doing their task than a general purpose computer

Utility software

Performs additional tasks that the OS cannot

Defragmentation software

Over time files move, are deleted, change size. This leads to many small gaps appearing on the disk.

This makes the files harder to read because the read/write head has to move back and forth

This software reorganises data to put fragmented files back together and collects free space

Compression software

Makes files smaller by temporarily or permanently removing data from them

They need to be extracted before use

Encryption software

Encrypts data to stop 3rd parties accessing jt

A special key is needed to decrypt data

Backup software

Data may be lost accidentally or deliberately

Backup software prevents data loss

Makes regular copies of data and moves it to high capacity secondary storage or the cloud

Full backup

Making a copy of every file on a computer or network

Lots of storage and time consuming

Incremental backup

Makes a copy of every new file or changed file since the last backup

Thinks user can do with data using an OS

Name files

Save and delete files

Move files

Edit files

CPU purpose

Brain of the computer

Processes all data and instructions that makes the system work

Carries out the FDE cycle

Examples of read only discs

CD-ROM

DVD-ROM

BD-ROM

Examples of write once discs

CD-R

DVD-R

BD-R

Examples of rewritable discs

CD-RW

DVD-RW

BD-RW

Magnetic tapes

Type of magnetic storage

Comes in plastic cassettes and requires a special tape drive

Written sequentially so it is slow to find data

Character sets

Collections of characters that a computer recognises from their binary representation

ASCII

Character set that represents all letters, some numbers symbols and commands

7-bits per character → can represent 128

Extra 0 added to start of binary code so it fits into a byte

Codes are ordered

Unicode

Character set that tries to cover every possible character/symbol

Multiple bytes for each character

First 128 characters are the same as ASCII

Bitmap images

Store images as tiny dots called pixels

Colour of each pixel is represented as a binary code

Cannot maintain quality when resized

Colour depth

Number of bits used for each pixel in a bitmap image

Image resolution

Number of pixels in an image

Sometimes given as width x height

Metadata

Information stored in an image which allows a computer to recreate an image from binary data

Contains file format, height, width, colour depth, resolution

Vector images

Set of mathematical formulas and commands that a computer uses to reconstruct an image

Can be resized while maintaining quality as they don’t use any pixels

How sound is stored digitally

Recorded by a microphone as an analogue signal

Amplitude of the sound wave is sampled at regular intervals

Only certain values can be taken, according to the bit depth

Creates the curve digitally

Sample rate (sound)

How many samples are taken in a second

Commonly 44,100 Hz

Increased → better quality

Bit depth (sound)

Number of bits used for each sample

Increased → Closer to original recording

2 Types of compression

Lossy and Lossless

Lossy compression

Permanently removes data from a file

Eg: .mp3, .jpg

Lossless compression

Temporarily removes data from a file then restores it to original state when opened

Eg: .zip, .png