Data representation

Data storage measurements is order

Bit

Nibble

Byte

Kibibyte

Mebibyte

Gibibyte

Tebibyte

Pebibyte

Exbibyte

how much KiB is one MiB?

1024

What does data compression do?

Reduces size of the file

Benefits of compression

Quicker to transmit, upload and download

Not as much bandwidth needed

Fits in limitation of file size on apps

Less storage space needed

Lossy Compression

Reduces file size by permanently removing data like reducing image resolution or colour depth or sample resolution or sample rate

Loseless compression

Reduces file size without permanent loss of data like run length encoding

How does lossless compression work?

Compression algorithm used such as Run length encoding

Repeating patterns are identified and indexed with their number of occurrences and their position

Why do computers use binary?

Any form of data needs to be converted to binary to be used by a computer

Computers process data using switches or logic gates

These only use 2 states, on or off, 1 or 0

This is then stored in registers

Binary is base…

2

Hexadecimal is base…

16

Denary is base…

10

Area in Computer Science where hexadecimal is used

URLs

MAC addresses

Colour codes

Benefits of hexadecimal

Can represent 16 bit words as only 4 hexadecimal digits

Easy to convert back to binary if necessary

Overflow error

Value is greater than 255 in an 8 bit register

Computer has a predefined limit that it can represent or store for example 16 bit

If a value outside this limit is returned an overflow error happens

Most significant bit

The bit with the highest value

Least Significant Bit

The bit with the lowest value

In two’s compliment what is the value of the most significant bit

Negative

How to do two’s compliment method?

Write positive number in binary

Invert all the bits

Add one

Why may programmers use hexadecimal?

Quicker to write and read

Takes up less space of the screen

Quicker and easier to debug

Less likely to make a mistake

How is text converted from analogue to digital?

Character set is used such as ASCII or binary

Each character has its own unique binary value

Unicode vs ASCII

Unicode has a greater range of unique characters and symbols like different languages and emojis

ASCII has fewer characters

ASCII covers limited set of languages

ASCII requires 7/8 bits per character, Unicode has 16/32 bits per character

How does a computer represent sound?

Analogue sound wave is recorded using a microphone

Sound wave is sampled measuring height and amplitude

Each amplitude has a unique binary value

Sample rate is set which is the number of samples taken per second

Sample resolution is set which is the number of bits used for each sample

Each sample converted to binary

Sample rate

Number of samples taken per second

Sample resolution

Number of bits per sample like 16 bits.

Provides variation in amplitude that can be stored for each sample.

Determines how loud or quiet the sounds are which can be recorded

Why do analogue sounds and text and images have to be converted to digital

Computer can only process binary data.

How can accuracy of recording increase, and what does it cause?

Sample rate increase and resolution increase making file size increase

Image

Series of pixels that are converted to binary

Image resolution

Number of pixels in an image, number of pixels up times pixels wide, dimensions of an image

Colour depth

Number of bits used to represent each colour

How do you increase quality of an image and what does it cause

Increased resolution and colour depth causing increased file size

Pixel

One square/ one circle of a colour/ smallest component of the image

Benefits of increased colour depth of image

Image will be more detailed

Closer to the actual contents of the image in real life

It will have a greater range of colours