COMPUTING GCSE AQA PAP

What can binary represent

Text, numbers, pictures, sound

Binary used how

Used by computers to represent all data

Hexadecimal used how

To represent larger numbers than binary

Hexadecimal uses

Colour values, MAC adress

How to divide denary to hex

Divide num by 16 and write the answer and the remainder.

Divide the answer by 16 again and write down the answer and the remainder.

Keep going until you reach 0

Read the remainders from bottom to the top

Convert each remainder into hex.

How to binary to hex

Write binary number across two separate tables of 8,4,2,1

For each table, add up the numbers which have a 1 beneath them

Convert each number to hexadecimal

A in hexadecimal

10

B in hexadecimal

11

C in hexadecimal

12

D in hexadecimal

13

E in hexadecimal

14

F in hexadecimal

15

Denary to hex

Divide the number by 16 and write both the answer and remainder.

Divide the answer by 16 again and write down both the answer and the remainder.

Keep going until you reach 0

Convert each remainder to hex

A bit

The most basic unit of data measurement

0 or 1

a byte

8 bits

How many bytes in a KB

1024 bytes

How many kilobytes in a MB

1024 kilobytes

How many megabytes in a GB

1024 megabytes

How many gigabytes in a TB

1024 gigabytes

Binary addition 0+0 =

0

Binary addition 1 + 0 =

1

Binary addition 1 + 1 =

10

Binary addition 1 + 1 + 1 =

11

multiply by 2 in a binary shift

1 place to the left

Multiply by 4 in binary shift

2 places to the left

Divide by 2 binary shift

1 place to the right

Divide by 4 binary shift

2 places to the right

When will the computer use a character set

When storing and transmitting characters

ASCII bits

7 bits, 128 characters

ASCII disadvantage

Too small to hold every character and symbol in english and other languages

Unicode bits

16 bits and 65,536 characters

unicode advantages

More characters than ASCII

Same character codes as ASCII until 127

Includes additional symbols and emojis

Colour depth

The number of bits used to store the colour of a single pixel in a digital image

Image file and colour depth

The greater the colour depth, the larger the image file will be

Image size

Measured in the number of pixel used

Written as pixels wide x pixels high

File size formula

Height in pixels X width in pixels X colour depth in pixels

(divide by 8 will give value in bytes)

amplitude

The height of the sound wave at the time it was sampled

Amplitude and sound

The higher the amplitude the louder the sound

Sample rate

The number of samples taken in one second

Sample rate measured in

Hertz

Hertz and sample rate

1 hertz = 1 sample per second

Sampling and files

Small sampling interval = high sample rate = better quality sound file = larger file

Sample resolution

The number of bits used to store each sample

High sample rate

More accurate representation

More space needed - larger file size

Calculating sound files sizes

Sampling rate X sample resolution X seconds

Compression

Ways to reduce the amount of storage space required for data

Lossy compression

Data is lost and the original contents of the file can be completely recovered

Lossless compression

No data is lost and the original contents of the file can be completely recovered

Cons of lossless compression

Larger file sizes compared to lossy

Pros of lossless compression

Original quality maintained, data integrity

Lossless compression best used for

Text documents, software, medical records, professional photos, backups

Lossless compression examples

ZIP, PNG, FLAC, TIFF

Lossy compression pros

V small files, faster loading, less bandwidth

Lossy compression cons

Irreversible data loss, blurriness/blockiness

Lossy compression best for

Streaming video/audio, web images

Lossy compression examples

MP3, JPEG, MP4

Huffman coding compression method

Lossless

Huffman coding

A way to reduce the number of bits needed to send or store a message

Creating a huffman tree

Count how many times each character appears in the string

Add together the number of the two least common characters in a new block and label it with the total

Move the new block into the right place in the list based on its number

Repeat steps 2&3 until only one block remains

Label the branches in the tree working from the top down

Label the branches going in one direction 1 and the other 0

Calculating bits needed to store hoffmann compressed strings

Take length of the bit pattern for each character

Multiply it by the times the pattern is used

Add this together for each charachter

Calculating the bits needed to store uncompressed ASCII

number of characters x7

Run length encoding

Relies on original data having many repeating digits

Finds patterns in the original data to save space

Run length encoding compression method

Lossless compression

Hardware

The physical components of a computer

Hardware examples

Monitor, CPU, RAM, keyboard

Software

The programs and applications which run in the computer

Software examples

OS, games, word processor

AND boolean operator symbol

AND boolean operator

Two conditions must be met for the statement to be true

OR boolean operator symbol

OR boolean operator

at least one component must be met for the statement to be true

NOT boolean operator symbol

NOT boolean operator

Inverts the result

XOR boolean operator symbol

XOR boolean operator

exclusive or only output if 1 is true not both

AND boolean written as

‘.’

OR boolean written as

‘+’

NOT boolean written as

‘-’ (above the letter)

XOR boolean written as

‘⊕’

Trace tables

Test's algorithms for logic errors

System software

Controls hardware, allows other programs to run, provides an interface for the user to interact with the computer, maintains the computer system

Examples of system software

OS, utility software

Operating system function

Handles key hardware functions and provides a foundation for the user to interact with the computer and for other applications to run

File management

Allows users to find and manage data stored by the computer

controlled by OS

Process management

Allows users to run applications such as web browsers or word processors

Allocates use of main memory and CPU between processes

Controlled by OS

Peripheral management

Manages input and output between peripherals and a process

Uses device drivers to communicate with drivers

Controlled by OS

User management

acess levels control access to systems for security

Controlled by OS

Utility software

Helps with upkeep and maintenance of the system

File repair

Scans disk surface for damage

Can sometimes repair corrupt files

Type of utility software

Backups

Copies data for backup

Allowing damaged data to be restored

Type of utility software

Data compression

Reduces file size using algorithms

Lossless and lossy

Type of utility software

Defragmentation

Files on a disk are broken down into a series of segments

Rearanges fragmented segments so they are stored next to each other - decreases read/write time and improbes performance

Type of utility software

Anti-malware

Protects against viruses, spyware, and any other unwanted software

Type of utility software

Machine code

Processors understand it

Each type of processors has its own specific machine code

Consists of 1s and 0s

Low level programming language

Machine code cons

V difficult to learn, write, debug

Assembly language

Uses mnemonics

Must be translated into machine code for execution

Low level programming language

When assembly language used

in embedded systems

Commonly used to program device drivers

Assembly code pros

Easier for humans to understand and program than machine code

Assembly code cons

still quite difficult to learn

Advantages of low level programming languages

More tasks are possible

More flexible

Direct instructions

Less limited

More efficient