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Edexcel GCSE Computer Science (1CP2) Exam Questions

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4 questions · 8 marks

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1Describe2 marksCharacter Sets Swap Remove

Uppercase letters are represented in a computer using 7-bit ASCII codes.

Describe how the ASCII codes for the uppercase letters A to Z are arranged.

[2 marks]
Mark scheme

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

  • The codes run in alphabetical order/consecutively (1) so each letter has a code one more than the letter before it (1)
  • A has the code 65 and Z has the code 90 (1) so the codes for the letters in between increase by 1 each time (1)
  • The letters are stored in sequence (1) so B is A + 1, C is B + 1 and so on (1)

Accept the codes given in denary (65, 90) or as 7-bit binary (1000001, 1011010).

Do not accept 'the codes go up' or 'the codes are in order' on its own, as neither gives the step of 1 or links one letter to the next.

Do not accept 'each uppercase letter has a different code' on its own, as this does not describe the arrangement.

Example answers and how they were marked
Full marks2/2

The codes are in alphabetical order, so B is one more than A and C is one more than B.

Why: Codes are consecutive/in order (1) with the linked step of one more for each letter (1).

Some marks1/2

A is 65 and Z is 90.

Why: Gives the first half of the linked pair, the start and end codes (1), but does not give the linked development, the increase of 1 between letters (0).

No marks0/2

The ASCII codes for uppercase letters go up.

Why: 'Codes go up' on its own gives no step of 1 and no link to the next letter, so it is not creditworthy (0) under the 'Do not accept' line.

2Explain2 marksCharacter Sets Swap Remove

The ASCII code for the uppercase letter A is 65, which is stored as the 7-bit pattern 1000001.

Explain why the lowercase letter a is stored using a different 7-bit pattern.

[2 marks]
Mark scheme

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

  • The computer needs to tell/distinguish the uppercase A from the lowercase a (1) because each different character has its own unique 7-bit code/pattern (1)
  • A and a are different characters (1) so each needs a different 7-bit pattern to be stored and displayed correctly (1)
  • If A and a had the same 7-bit pattern (1) the computer could not tell which character to display (1)

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

Do not accept 'because they are different letters/cases' without saying they need different/unique codes or that the computer must tell them apart.

Do not accept 'because A is a capital letter' on its own.

Do not accept 'because the codes are different numbers' or '65 is not 97' without linking to the need to tell the characters apart or to unique codes.

Example answers and how they were marked
Full marks2/2

Each character needs its own unique code, so the computer can tell that A and a are different characters and display the right one.

Why: Gives the point that the computer must tell A and a apart (1) and links it to the reason that each character needs its own unique code (1).

Some marks1/2

The computer must be able to tell the difference between uppercase and lowercase letters.

Why: Gives the point that the computer must tell the two characters apart (1) but gives no linked reason about unique codes or different 7-bit patterns.

No marks0/2

Because A is a capital letter and a is lowercase.

Why: Only states that the letters are different cases, which the mark scheme says is not accepted without saying they need unique codes or that the computer must tell them apart.

3Explain2 marksImages Swap Remove

A bitmap image uses a colour depth of 8 bits. Each pixel is stored as a binary value.

Explain how the colour of a pixel is represented in a bitmap image.

[2 marks]
Mark scheme

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

  • Each pixel is stored as a binary value/code (1) which represents/maps to a colour (1)
  • The binary value is used to look up a colour in a palette (1) so the pixel can be displayed in that colour (1)
  • A bit pattern is assigned to each colour (1) and each pixel stores the bit pattern for its colour (1)
  • The number of bits per pixel sets how many different colour codes exist (1) so each code can represent a different colour (1)

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

Do not accept 'pixels are binary' or 'the image is made of 1s and 0s' without saying a pixel's colour is represented by a binary value.

Do not accept RGB values stored as denary or hexadecimal.

Example answers and how they were marked
Full marks2/2

Each pixel stores a binary value; this value is used to look up the pixel's colour in a palette.

Why: Linked point (1) and reason (1): a binary value is stored for each pixel and maps to a colour.

Some marks1/2

A bit pattern is assigned to each colour.

Why: One mark for stating that colours have bit patterns; it does not say that each pixel stores the pattern for its colour.

No marks0/2

Each pixel stores the RGB colour as denary numbers between 0 and 255.

Why: Bitmap pixels are stored in binary, not as denary values; this common misconception earns no mark.

4Explain2 marksCharacter Sets Swap Remove

A computer system uses a 4-bit code to represent the characters typed on its keyboard.

Explain one limitation of using 4 bits to represent characters.

[2 marks]
Mark scheme

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

  • Only 16 different characters can be represented (1) so there are not enough characters codes for every letter of the alphabet (1)
  • 4 bits give only 16 different combinations (1) which is not enough for the uppercase letters, lowercase letters, digits and symbols on a keyboard (1)
  • More than 16 characters are needed on a keyboard (1) so some letters, digits or symbols cannot be represented (1)
  • The number of character codes available is limited to 16 (1) because 4 bits give 2 to the power of 4 combinations (1)

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

Calculating that 4 bits give 2 to the power of 4 = 16 combinations can earn either the point or the linked reason, provided the other half of the answer says what this means (too few characters/codes).

Allow an expansion that names only the letters of the alphabet, e.g. there are not enough character codes for the 26 letters (1).

Do not accept '4 bits can only store 4 characters' (the number of bits is not the number of characters).

Do not accept 'it can only store 16 bits' (16 is the number of character codes/combinations, not the number of bits).

Do not accept 'not enough memory/storage' (the limitation is the number of character codes, not the amount of storage).

Do not accept 'it is limited/smaller' without saying how many characters/codes are available or what cannot be represented.

Example answers and how they were marked
Full marks2/2

Only 16 different characters can be represented, so there are not enough character codes for all 26 letters.

Why: Gives the point that only 16 characters can be represented (1) and links it to the reason that this is fewer than the letters needed (1).

Some marks1/2

Only 16 different characters can be represented.

Why: Gives the point that only 16 characters can be represented (1) but does not explain what cannot be represented.

No marks0/2

It can only store 4 characters because there are 4 bits.

Why: Misconception that the number of bits equals the number of characters, which the mark scheme says not to accept; no creditworthy point.

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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