Data representation - Text, sound, images and compression (paper 1)

Question 1

include character sets

how and why does a computer represents text, using Unicode

Answer 1

• allows for a greater range of characters and symbols than ASCII, including different languages (Russian, Chinese, Arabic) and emojis

Question 2

what is the disadvantage of Unicode

Answer 2

• Unicode requires more bits per character than
  ASCII
• requires 16 bits per character

Question 3

how many bits does ASCII use to represent a character

Answer 3

7 - allows up to 128 characters

Question 4

how many bits does Extended ASCII use to represent a character

Answer 4

8 - allows up to 256 characters

Question 5

why was extended ASCII introduced

Answer 5

• additional characters in the set including symbols, common foreign languages + mathematical symbols introduced

Question 6

what is character set

Answer 6

• each character of the keyboard has a binary code
• All of the characters, letters, numbers that is recognised by a computer system

Question 7

Two standard character sets in common use are:

Answer 7

• American Standard Code for Information Interchange (ASCII)
• Unicode

Question 8

does a ‘space’ count as a character

Answer 8

YES - it counts as one Byte

Question 9

5 key stages

how are analogue sounds recorded

Answer 9

• analogue sound must be digitally recorded and converted into binary
• amplitude emitted is measures and recorded / sampled at regular intervals
• how often it is recorded is the sample rate
• accuracy to which the height is recorded = sample resolution
• duration of the recording will affect file size

Question 10

what does the sample resolution have an affect on

Answer 10

the quality of the recorded sound when played back
- file size of the recording

Question 11

what also increases when the sample rate and sample resolution increase

Answer 11

accuracy and file size increase

Question 12

what does the sample resolution measure

Answer 12

number of bits per sample - accuracy to which the height is recorded

Question 13

what does the sample rate measure

Answer 13

the number of samples taken
in a second

Question 14

what is sample rate measured in

Answer 14

Hertz

Question 15

Sound file size = ?

Answer 15

(Number of samples per second ) x (sample rate) x (Length of sample in seconds)
- always divide by the number of the bit sample

Question 16

what is a image made up of

Answer 16

a series ofpixels that are converted to binary, which is processed by a computer

Question 17

image resolution = ?

Answer 17

number of pixels (px) in the image

Question 18

colour depth = ?

Answer 18

number of bits used to
represent each colour

Question 19

if the file size and image quality increases what is the cause

Answer 19

resolution and colour depth increase

Question 20

Image file size = ?

Answer 20

(width in pixels x height in pixels x colour depth) / 8 gives size in bytes

Question 21

what is the purpose of data compression

Answer 21

• reduces file size by removing repeated / unnecessary data

Question 22

what is the impact of having smaller data file size

Answer 22

• less bandwidth required
• less storage space required
• shorter transmission time

Question 23

what is lossless compression and how does it compress data

Answer 23

reduces the file size
without permanent loss of data –> e.g. run length
encoding (RLE)

Question 24

what is lossy compression and how does it compress data

Answer 24

reduces the file size by
permanently removing data –> reducing
resolution or colour depth, reducing sample rate
or resolution

Question 25

3

what are the advantages of lossy compression

Answer 25

• smallest file size
• least transmission time
• reduces Internet traffic + collision

Question 26

advantages of lossless compressions

Answer 26

• original quality preserved / no info or data is lost

Question 27

disadvantages of lossy compression

Answer 27

• detail permanently lost by reducing colour depth, resolution or sample rate

Question 28

disadvantages of lossless compression

Answer 28

less significant reduction in file size

Question 29

examples of lossy compression

Answer 29

• music streaming
• online images / video
• image libraries on devices or in the Cloud

Question 30

examples of lossless compression

Answer 30

• text documents
• electronic books
• hgh resolution print documents

Question 31

what is the RLE algorithm

Answer 31

It groups repeating pieces of data and stores them using significantly less data

Question 32

using the RLE algorithm rewrite: 00000111000001111100

Answer 32

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