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Edexcel GCSE Computer Science (1CP2) Exam Questions

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4 questions · 12 marks

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1Multiple choice1 markCharacter Sets Swap Remove

Characters are encoded using 7-bit ASCII.

Identify the number of different characters that can be represented using 7-bit ASCII.

[1 mark]
  • A64
  • B127
  • C128
  • D256
Mark scheme
  • C 128 (1)
  • The only correct answer is C. The correct answer is 128.
  • A is not correct because 6 bits give only 64 different combinations
  • B is not correct because 127 is the largest 7-bit value, not the number of characters that 7 bits can represent
  • D is not correct because 256 characters need 8 bits, as used by 8-bit extended ASCII
Example answers and how they were marked
Full marks1/1

C 128

Why: Selects the only correct option (1): 7 bits give 2 to the power of 7, which is 128 different characters.

No marks0/1

D 256

Why: Near miss scoring 0: 256 is the number of characters that 8 bits give in extended ASCII, not 7-bit ASCII.

No marks0/1

B 127

Why: Misconception scoring 0, the off-by-one error the examiners' report describes: 127 is the largest 7-bit value, but 7 bits give 128 different characters.

2Short recall2 marksEmbedded Systems Swap Remove

A digital camera contains an embedded system.

Give two functions that the embedded system performs in the digital camera.

[2 marks]
Mark scheme

Award one mark for any of the following up to a maximum of two marks:

  • Focus the lens/autofocus (1)
  • Control the shutter (speed) (1)
  • Control the flash/decide when the flash is needed (1)
  • Measure the light level to set the exposure/the aperture (1)
  • Stabilise the lens/image stabilisation (1)
  • Zoom the lens in and out (1)
  • Detect a face/smile (1)

Do not accept 'take a photograph'/'take a picture'/'capture an image', as taking photographs is the function of the camera, which is given in the question.

Do not accept 'press the button' as this is an action of the user, not a function performed by the embedded system.

Do not accept vague answers such as 'use the camera', 'turn the camera on and off' or 'make the camera work', which do not name a function that the embedded system performs.

Example answers and how they were marked
Full marks2/2

It focuses the lens and decides when the flash should fire.

Why: Focus the lens (1) and control the flash (1).

Some marks1/2

It controls the zoom and takes a picture when the button is pressed.

Why: Zoom the lens credited (1); 'takes a picture' is not accepted because taking photographs is the function of the camera, which is given in the question, and 'press the button' is the user's action, not a function of the embedded system.

No marks0/2

It takes a picture when the button is pressed and it makes the camera work.

Why: No mark: 'takes a picture' repeats the camera's function given in the question, 'press the button' is an action of the user, and 'makes the camera work' is too vague to name a function.

3Calculate3 marksAdding Binary Numbers Swap Remove

Binary patterns can represent numbers.

(a)

Complete the table to show the 8-bit result of the binary addition.

[2 marks]
1286432168421
11011011
11011100
Mark scheme

Award one mark for each correct nibble in the correct order:

  • 1011 (1)
  • 0111 (1)

0 marks if the response is not 8-bit binary.

Ignore a carry shown beyond the eighth bit.

Example answers and how they were marked
Full marks2/2

1011 0111

Why: 219 + 220 = 439, which needs 9 bits; the 8 bits that are kept are both correct (2).

Some marks1/2

0000 0111

Why: Forgets to carry the 1s. The second nibble is correct (1); the first is not.

No marks0/2

1101 1111

Why: Never carries. Neither nibble is correct.

(b)

State the name of the error that occurs when this addition is carried out.

[1 mark]
Mark scheme

Award one mark for:

  • overflow (error) (1)
Example answers and how they were marked
Full marks1/1

Overflow

Why: The result needs more bits than are available (1).

No marks0/1

Underflow

Why: A near miss: the result is too big for 8 bits, not too small.

No marks0/1

A syntax error

Why: A syntax error is a mistake in a program's code, not in arithmetic.

4Discuss6 marksFile Management Swap Remove

A small business has one computer with a single hard disk. Two employees save documents and photographs to it every day. The operating system manages the disk.

Discuss why the operating system needs to manage where files are stored on the disk.

Your answer should include:

  • how the operating system allocates disk space when a file is saved
  • how the operating system keeps track of each file
  • what could happen if the operating system did not manage files
[6 marks]
Mark scheme

Indicative content

Allocating space

  • The operating system checks that there is enough free space before a file is saved, so a large photograph does not make the save fail.
  • The operating system finds free space on the disk and allocates it to the new file, so the file's data has somewhere to be written.
  • Disk space is allocated so that a file is not written on top of data that already belongs to another file.
  • When a file is deleted, the operating system marks its space as free so it can be used again by the next document that is saved.

Keeping track

  • The operating system keeps a record of the name, size and location of every file, so it knows where each file is stored.
  • The record is updated whenever a file is saved, renamed or deleted, so it still matches what is on the disk.
  • The operating system uses this record to find a file again, so an employee can open a document or photograph that was saved earlier.
  • The record lets the operating system tell the two employees' documents and photographs apart, even though they are all on the same disk.

Without this management

  • Two files could be given the same space, so one document would overwrite another and the work would be lost.
  • The operating system would not know where a file is stored, so a saved document could not be found and opened again.
  • Space used by deleted files might never be freed, so the disk would fill up and new files could not be saved.

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 both the allocation of space and the tracking of files, with at least one consequence of no management linked to its cause. Reference to a file being split across blocks that are not next to each other, or to the record holding the location of each block, is Level 3 detail and is not required.

Basic, unlinked points with no application to the business's documents or photographs, and a consequence such as 'files would be lost' with no cause given, are limited to Level 1; to reach Level 2 a point must be linked to a reason (for example, the record is kept so a document can be found again) and be applied to the context. Do not accept defragmentation, process scheduling, user management, peripheral management, or backup and antivirus scanning, as file management.

Example answers and how they were marked
Full marks6/6

Before a document is saved, the operating system checks that there is enough free space on the single disk, so a large photograph cannot make the save fail. It then finds free space and allocates it to the new file, making sure it does not write over data that already belongs to another file. The operating system keeps a record of the name, size and location of every file and updates it whenever a file is saved or deleted. It uses this record to find a file again, so an employee can open a document that was saved earlier. Without this, the two employees could be given the same space, so one document would overwrite the other, or the operating system would not know where a file is stored and the business could not find its work again.

Why: Covers both allocation (free space check, free space given to the file, no overwriting) and tracking (record of name, size and location, updated on save, used to find the file), applies it to the business's single disk and its two employees' documents and photographs, and links the consequences of no management to their causes: Level 3.

Some marks2/6

The operating system decides where on the disk a file is saved. It also keeps a record of where each file is stored. Without this, files would be lost.

Why: Two basic points are made: space is allocated when a file is saved, and a record of where each file is stored is kept. Neither is linked to a reason, there is no application to the business's documents and photographs, and 'files would be lost' is given with no cause: Level 1, top of the level.

Some marks1/6

The operating system puts files in the right place so the disk does not get full. It also defragments the disk to make the files smaller.

Why: One basic point about the operating system placing files on the disk so it does not fill up (Level 1). Defragmentation is not file management and does not make files smaller, so it is not credited: Level 1.

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