iGCSE CS - Data Representation

All data must be converted to — before a computer can understand and process it

Binary

Define Denary number system

Denary is a number system that is made up of 10 digits, 0-9

It is a base-10 number system

Define binary

Binary is a base-2 number system, made up of 1s and 0s.

Define Hexadecimal

Hexadecimal is a number system made up of 16 digits - 10 numbers (0-9) and 6 letters (A-F)

Base-16 number system

2 reasons why hexadecimal > binary

• more bits in binary make it harder for humans to read

• binary is more prone to errors when being copied

3 examples of where hexadecimal is used

• MAC addresses

• Color codes

• URLs

MAC addresses consist of 12 — digits = 48 — digits. Writing down or performing calculations with 48 — digits makes it very easy to make a mistake.

Hexadecimal

Binary

Binary

A typical hexadecimal color code consists of — hexadecimal digits = — binary digits

6

24

Define Character Set

All the characters and symbols that can be represented by a computer system. Each character is given a unique binary code and are ordered logically.

A character set provides a — for computers to — and…

Standard

Communicate and send/receive information

Name the 2 common character sets

• ASCII

• UNICODE

ASCII uses — bits, providing maximum — characters

• 7 bits

• 128 characters

Extended ASCII uses — bits, providing — maximum characters. It provides essential characters such as — — and more recent symbols

• 8 bits

• 256

• mathematical operators

List the 3 limitations of ASCII and Extended ASCII

1. ASCII has a limited n.o characters so it only represents the English alphabet and numbers, along with some characters

2. Cannot represent characters from other languages

3. No modern symbols or emojis

UNICODE uses a minimum of — bits, providing — characters max. It can represent characters from all major languages in the world.

16

65,536 characters

One drawback of ASCII

Uses more storage space

Describe the process of Analogue to Digital conversion

1. Measure amplitude of the analogue sound wave at a point in time, called samples

2. Each measurement/sample generates a value which is represented in binary and stored

3. Using the samples, a computer is able to generate a digital version of the original wave

4. Digital wave is stored on secondary storage and can be replayed back at any time by reversing the process

Define sample rate + unit of measurement

The amount of samples taken per second of the analogue wave

Hertz (Hz)

Samples are taken each second for the — of the sound.

Duration

The higher the sample rate, the…

Closer to the original sound wave the digital version looks

Define sample resolution

Number of bits stored per sample of sound

A bitmap image is made up of squares called —

Pixels

A pixel is the — — of a bitmap image

Smallest element

Each pixel is stored as..

A binary code - this is unique to colour of each pixel

Define resolution and how to calculate

The total number of pixels that make up a bitmap image

Image height x image width

Define colour depth

Number of bits stored per pixel in a bitmap image

Dependent on the number of colours needed in the image

How to calculate amount of colours from the colour depth?

2 to the power of n, n being colour depth

As resolution and colour depth increases, the file size — on — storage

• increases

• secondary

Simply name all the units of data storage in increasing order first

• Bit

• Nibble

• Byte

• Kibibyte

• Mebibyte

• Gibibyte

• Tebibyte

• Pebibyte

• Exbibyte

How many bits in a nibble

4

How many bits in a byte

8

How many bytes in a kibibyte

1024

Describe converting between units

Give the 2 formulae for calculating the size of a bitmap image

Resolution x Colour Depth

Image Width x Image Height x Colour Depth

Formula for calculating size of a sound file

Sample Rate x Duration x Sample Resolution

Define Compression

Reducing the file size so that it takes up less storage space on secondary storage

3 effects of compression

• Less storage space required

• Less bandwidth required

• Shorter transmission time

Name 2 types of compression

Lossy and lossless

Define Lossy compression

• When data is lost in order to reduce the size on secondary storage

• Greatly reduces the file size but at the expense of losing quality

• Irreversible

Define lossless compression

• when data is encoded in order to reduce the file size on secondary storage

• File size reduction not as dramatic

• Reversible

Define Run Length Encoding (RLE) and e.g

A form of lossless data compression that condenses identical elements into a single value, with a count

E.g: AAAABBBCC is compressed to 4A3B2C

RLE is used in — — to compress sequences of the — —

• bitmap images

• same colour