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Edexcel GCSE Computer Science (1CP2) Exam Questions

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2 questions · 8 marks

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1Describe2 marksImages Swap Remove

A bitmap image is stored using 2 bits for each pixel.

Describe why using 2 bits for each pixel can limit the image.

[2 marks]
Mark scheme

Award up to two marks for a linked description such as:

  • Two bits give only four possible binary values (1) so at most four colours can be represented (1)
  • Only 2^2 = 4 colours can be stored (1) so colours in the original image may be lost/changed (1)
  • There are not enough bit patterns for more than four colours (1) so the image cannot show all the colours it needs (1)
  • Each pixel has a limited set of codes (1) so similar colours may become the same colour (1)

Do not accept 'the image will be low resolution' or 'it will be poor quality' alone.

Do not award responses about file size.

Example answers and how they were marked
Full marks2/2

Two bits give only four binary values, so the image can use at most four colours.

Why: Point (1) that two bits give only four binary values and development (1) that at most four colours can be represented.

Some marks1/2

Two bits can only represent four colours.

Why: Point (1) that only four colours can be stored, but no linked development about colours being lost or changed.

No marks0/2

The image will be low resolution because there are not enough bits.

Why: No credit: 'low resolution' alone is not accepted as a limitation of using 2 bits per pixel.

2Discuss6 marksCharacter Sets Swap Remove

A library is digitising its catalogue. The titles of books and the names of authors are stored as text.

Discuss how 7-bit ASCII is used to encode the text in the library catalogue.

Your answer should include:

  • how characters are mapped to codes
  • why 7 bits are used for each character
  • the benefits of using ASCII for the catalogue.
[6 marks]
Mark scheme

Indicative content

How characters are mapped to codes

  • Each character in a book title or author name is given a unique 7-bit binary code from the ASCII character set.
  • The letter A, for example, is stored as the code 1000001 and the letter B as 1000010, so the catalogue can store letters as binary.
  • Uppercase letters, lowercase letters, digits, punctuation and the space character each have their own ASCII code.
  • The same character always uses the same code, so the text can be stored and read back correctly by the library system.

Why 7 bits are used for each character

  • Seven bits give 2 to the power of 7, which is 128 different bit patterns, and this is enough to represent the letters, digits and punctuation needed in the catalogue.
  • A standard keyboard has around 98 characters, so 6 bits would give only 64 codes and would not be enough.
  • Using a fixed 7 bits per character means every character takes the same amount of storage, which makes the catalogue file simple to process.

Benefits of using ASCII for the catalogue

  • ASCII is a standard character set, so the catalogue data can be exchanged between different computers and software.
  • Author names and titles entered on one system will display correctly on another system that uses ASCII.
  • ASCII uses only 7 bits per character, so the catalogue takes less storage than a character set that uses more bits.
  • It is simple to encode and decode because each character has a single fixed code.

Levels

  • Level 0 (0 marks): No rewardable content.
  • Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
  • Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
  • Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Do not accept 8 bits or 256 characters as features of 7-bit ASCII; these are extended ASCII.

Example answers and how they were marked
Full marks6/6

Each character in a catalogue title or author name is given its own 7-bit ASCII code. For example, the letter A is 1000001 and the letter B is 1000010, so the library can store the text as binary. Seven bits give 128 different codes, which is enough for uppercase and lowercase letters, digits, punctuation and spaces. Six bits would give only 64 codes, which would not be enough for all the characters in the catalogue. ASCII is also a standard character set, so the catalogue data can be exchanged between different computers and will display correctly. Because each character uses only 7 bits, the catalogue also takes less storage than it would with a character set that uses more bits per character.

Why: Covers all three bullets with sustained application: mapping and example codes; 7 bits give 128 codes and why 6 bits is insufficient; standardisation and storage benefits. Level 3.

Some marks4/6

ASCII gives each character a unique code. For example, A is stored as 1000001 and B is stored as 1000010. Seven bits are used for each character because seven bits give 128 codes, which is enough for the letters and punctuation in the catalogue. The library can store titles and author names as binary.

Why: Covers mapping and the 7-bit reason with some application, but does not discuss the benefits of ASCII for the catalogue. Level 2.

Some marks1/6

ASCII is a programming language that gives each letter a binary code. It uses 8 bits for each character, so it can store 256 characters. This means it can store every book title in the library.

Why: A basic point that letters are given binary codes is credited, but the answer treats ASCII as a programming language and uses 8 bits/256 characters, which are misconceptions. Level 1.

Questions by topic

2.1 Binary

Build a paper on this topic 58
Adding Binary Numbers 6 questions Binary and Hexadecimal Basics 10 questions Binary Shifts 6 questions Binary to Denary Conversion 6 questions Binary to Hexadecimal Conversion 6 questions Denary to Binary Conversion 6 questions Denary to Hexadecimal Conversion 6 questions Denary to Negative Binary Conversion 6 questions Hexadecimal to Binary Conversion 6 questions

2.2 Data representation

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Character Sets 18 questions Images 19 questions Sound 19 questions

2.3 Data storage and compression

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Compression 18 questions Units & Conversion 6 questions

3.1 Hardware

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Embedded Systems 17 questions Fetch Decode Execute Cycle 15 questions Primary Memory 15 questions Secondary Memory 15 questions Stored Program Computers 15 questions

3.2 Software

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File Management 18 questions Memory Management 16 questions Peripheral Management 11 questions Process Management 12 questions Purpose & Function of Operating Systems 17 questions Software Basics 13 questions User Management 18 questions Utility Software 19 questions

3.3 Programming languages

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Low and High Level Languages 19 questions Translators 18 questions

4.1 Networks

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Addressing 16 questions LANs & WANs 16 questions Network Speed 5 questions Packet Switching 16 questions Protocols & Layers 17 questions The Internet 16 questions Topologies 17 questions Wired Connections 17 questions Wireless Connections 18 questions

4.2 Network security

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Network Security Risks 18 questions Preventing Network Security Risks 18 questions

5.1 Environmental

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E-waste 17 questions Manufacturing Technology 19 questions

5.2 Ethical and legal

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Data Protection Act 17 questions Impact of AI 18 questions Intellectual Property 18 questions Software Licences 18 questions

5.3 Cybersecurity

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Malware 18 questions Social Engineering 18 questions

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