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Edexcel GCSE Computer Science (1CP2) Exam Questions

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3 questions · 10 marks

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1Explain2 marksCharacter Sets Swap Remove

Characters typed on a keyboard are stored using ASCII.

Explain how the computer encodes the letter A using ASCII.

[2 marks]
Mark scheme

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

  • The computer looks up the character in the ASCII character set/table (1) to find the code that represents it (1)
  • Each character has its own unique ASCII code (1) so the letter A is converted to and stored as a 7-bit binary pattern (1)
  • ASCII uses 7 bits for each character (1) so A is stored as its ASCII code 1000001 (binary) / 65 (denary) (1)

The second mark requires a linked expansion, so a point on its own (e.g. 'A has the code 65') can only earn one mark.

For both marks, the expansion must follow/associate with the statement.

Accept an 8-bit pattern with a leading 0 (e.g. 01000001) as the binary code for A.

Do not accept 'the character is stored as text' without saying it is changed into a code/binary.

Do not accept a binary value on its own (e.g. 1000001) without saying that it is the ASCII code/that the character is converted to it.

Example answers and how they were marked
Full marks2/2

The computer finds the unique ASCII code for A, which is 65 in denary, and stores it as the 7-bit binary pattern 1000001.

Why: Linked point that A is given its unique ASCII code (1) and reason/expansion that it is converted to and stored as a 7-bit binary pattern (1).

Some marks1/2

The computer changes the letter A into a number.

Why: Gives the point that the character is given a code/number (1) but no linked expansion saying it is converted to binary or stored, so stays on one mark.

No marks0/2

The letter A is stored as the number 1 because it is the first letter of the alphabet.

Why: Wrong reason and no creditworthy point: it does not say that the character is given its ASCII code and converted to binary.

2Explain2 marksCharacter Sets Swap Remove

ASCII uses a fixed number of bits to represent each character.

Explain one reason why ASCII uses 7 bits to represent each character.

[2 marks]
Mark scheme

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

  • 7 bits give 128 different codes/combinations (1) which is enough to represent all the characters on a keyboard (1)
  • 7 bits allow 128 unique characters (1) so uppercase and lowercase letters, digits and punctuation can all be represented (1)
  • 6 bits give only 64 combinations (1) which is not enough for the number of characters on a keyboard (1)
  • A keyboard needs to represent more than 64 different characters (1) so 7 bits are needed to give the 128 combinations required (1)
  • A fixed number of 7 bits gives 128 possible codes (1) which is enough for the characters ASCII represents, so more bits are not needed (1)

For both marks, the expansion must follow/associate with the statement.

Do not accept 'because ASCII is 7-bit' or 'because 7 bits is enough' as these repeat the question without giving the number of combinations or saying what they allow.

Do not accept '7 bits give 256 characters'; 256 combinations come from 8 bits (extended ASCII).

Allow 'ASCII has 128 characters/codes' for the 128 point.

Example answers and how they were marked
Full marks2/2

7 bits give 128 different codes, which is enough for every letter, digit and punctuation symbol on a keyboard.

Why: Gives the point that 7 bits give 128 codes (1) and links it to the reason that this is enough for all the characters on a keyboard (1).

Some marks1/2

7 bits give 128 different combinations.

Why: Gives the point that 7 bits give 128 combinations (1) but does not say what this number of combinations allows, so the linked reason (1) is not earned.

No marks0/2

Because ASCII uses 7 bits so it can store 256 characters.

Why: Repeats the question and gives the wrong number of characters (256 is 8-bit extended ASCII), so there is no creditworthy point.

3Discuss6 marksImages Swap Remove

A handheld games console displays sprites. The console stores each pixel of a sprite using 4 bits. Designers want sprites that contain many shades of green and blue.

Discuss the limitations of using 4 bits to store each pixel of a sprite on the console.

Your answer should include:

  • the number of colours that can be represented
  • the effect on the appearance of the sprite
  • how the limitation could be managed.
[6 marks]
Mark scheme

Indicative content

Number of colours

  • 4 bits give 2^4 = 16 different binary values, so at most 16 colours can be stored for each pixel.
  • The console cannot store every shade that the designers want; colours outside the 16 must be approximated or left out.
  • Adding more bits per pixel would allow more colours, but this may not be possible on the console's hardware.

Effect on appearance

  • The sprite may show banding where a smooth change from green to blue should be.
  • A sprite that needs many shades, such as a detailed landscape, will look unrealistic or have blocks of colour.
  • Simple sprites with flat colours, such as a retro character, can still look acceptable.
  • The limitation is in the number of colours, not the number of pixels; resolution is a separate issue.

Managing the limitation

  • Designers can choose a palette of 16 colours that includes the most important greens and blues for the game.
  • They can design sprites with flat colours rather than smooth gradients.
  • They can use more bits per pixel for important sprites if the console allows it.
  • They can accept that some shades will be approximated and check that the sprite still looks clear on the console's screen.

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)

Level 3 responses must cover the number of colours and the effect on appearance.

Do not accept 4 bits give 4 colours or 8 colours.

Example answers and how they were marked
Full marks6/6

4 bits per pixel gives 2^4 = 16 different binary values, so each pixel can be only one of 16 colours. The designers want many shades of green and blue, but most of these cannot be stored exactly and must be approximated or left out. This can cause banding where a smooth change from green to blue should be, so a detailed sprite may look unrealistic. A simple sprite with flat colours could still look acceptable. The designers could choose a palette of 16 colours that includes the most important greens and blues, and design sprites with flat colours instead of gradients. Using more bits per pixel would allow more colours, but the console's hardware may not support this.

Why: Explains 2^4 = 16 colours and the limitation on shades, links this to banding and realism, and gives suitable ways to manage it in the console context. Sustained reasoning, so Level 3.

Some marks4/6

4 bits can store 16 colours. This means the sprite cannot have many colours. It might look bad if it needs lots of shades of green and blue. The designers could use fewer colours in the sprite.

Why: Correctly gives 16 colours and makes a simple link to the sprite's appearance and a way to manage it. There is little development of the effect or the management, so Level 2.

Some marks1/6

4 bits can store 16 colours. This means the sprite will have a low resolution, so it will look blocky. The designers should use a higher resolution to get more shades of green and blue.

Why: One correct point: 4 bits give 16 colours. The answer then confuses colour depth with resolution; increasing resolution would not provide more shades.

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

Build a paper on this topic 77
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

Build a paper on this topic 30
Malware 18 questions Social Engineering 12 questions

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