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Computer Science GCES EDEXCEL

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  1. Decomposition And Abstraction Edexcel
    2 主题
  2. Algorithms Edexcel
    11 主题
  3. Truth Tables Edexcel
    3 主题
  4. Binary Edexcel
    6 主题
  5. Data Representation Edexcel
    4 主题
  6. Data Storage And Compression Edexcel
    2 主题
  7. Hardware Edexcel
    5 主题
  8. Software Edexcel
    3 主题
  9. Programming Languages Edexcel
    2 主题
  10. Networks Edexcel
    7 主题
  11. Network Security Edexcel
    2 主题
  12. Environmental Issues Edexcel
    1 主题
  13. Ethical And Legal Issues Edexcel
    3 主题
  14. Cybersecurity Edexcel
    2 主题
  15. Develop Code Edexcel
    6 主题
  16. Constructs Edexcel
    4 主题
  17. Data Types And Data Structures Edexcel
    5 主题
  18. Operators Edexcel
    1 主题
  19. Subprograms Edexcel
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Exam code:1CP2

Limitations of Binary

What are the limitations of binary?

  • Binary representation is constrained by the number of available bits, for example, the number of available bits determines how the following are represented:

    • Characters

    • Images

    • Sound

  • The more bits, the greater range of unique values

  • The amount of unique values can be calculated with the formula 2number of bits, where 2 is the number base

Number of bits

Expression

Number of unique values

1

21

2

2

22

4

3

23

8

4

24

16

5

25

32

6

26

64

7

27

128

8

28

256

Characters

  • The number of bits limits the amount of available characters that can be represented

  • For example, using 5 bits would allow 32 unique characters to be represented which is not enough to handle the English language (26 x lowercase, 26 uppercase letters etc.)

Images

  • Modern computers use a minimum of 24 bits to represent high quality bitmap images

  • Three groups of 8 bits are used to represent the amount of red, green & blue in each pixel (RGB)

  • 24 bits = 16,777,216 unique colours

  • Lowering the amount of available bits would reduce the unique colours, reducing the overall quality of the image

Sound

  • CD has long been accepted as the standard for music quality, requiring 16 bits to be achieved (216 = 65,536)

  • Lowering the amount of available bits, for example in telephone calls reduces the quality of the sound (28 = 256)

  • This reduction is most evident in hold music used in telephone calls

Worked Example

State how many bits are needed to represent the 26 capital letters A to Z.

Give a reason for your answer [2]

Number of bits: ………………………………………………….

Reason: …………………………………………………………….

Answer

Number of bits: 5

Reason: 4 bits would allow for 16 which is not enough
OR
5 bits allows for 32 which is enough

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