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Edexcel GCSE Computer Science (1CP2) Exam Questions

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4 questions · 11 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 marksCompression Swap Remove

Images and sound can be stored using lossy compression.

Define the term lossy compression.

[2 marks]
Mark scheme

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

  • Reduces the size of a file (1)
  • Permanently removes/loses some data (1)
  • The original file cannot be recreated/restored exactly (1)

Allow 'some data is deleted/discarded and cannot be recovered' for the second mark.

Do not award the first mark where the response also states that no data is lost.

Do not accept 'removes repeated data' (this describes lossless compression).

Example answers and how they were marked
Full marks2/2

Lossy compression reduces the size of a file by permanently removing some data, so the original cannot be restored exactly.

Why: Reduces the size of a file (1); permanently removes some data (1); maximum two marks awarded.

Some marks1/2

It makes a file smaller.

Why: Reduces the size of a file (1); no reference to data being permanently lost.

No marks0/2

It makes a file smaller without losing any of the data.

Why: States that no data is lost, which describes lossless compression; the first mark is not awarded.

3Calculate2 marksAdding Binary Numbers Swap Remove

Binary patterns can represent numbers.

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

[2 marks]
1286432168421
10010110
01011100
Mark scheme

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

  • 1111 (1)
  • 0010 (1)

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

Example answers and how they were marked
Full marks2/2

1111 0010

Why: 150 + 92 = 242, carrying where a column adds to 2: both nibbles are correct (2).

Some marks1/2

1111 0011

Why: A slip in the last bit. The first nibble is correct (1); the second is not.

No marks0/2

1101 1110

Why: Writes 1 in every column with a 1 and never carries. Neither nibble is correct.

4Discuss6 marksUtility Software Swap Remove

A college has a room of older desktop computers. Each computer has a magnetic hard disk that is almost full. Staff have noticed that files on these computers take a long time to open because the disks have become fragmented.

Discuss the use of disk defragmentation software on these computers.

Your answer should include:

  • how files become fragmented
  • what defragmentation software does
  • the benefits and drawbacks of running it.
[6 marks]
Mark scheme

Indicative content

How files become fragmented

  • A file is saved into free blocks on the disk, so as files are deleted and new ones saved, one file can end up split across blocks in different places.
  • Large files are more likely to become fragmented because they may not fit into one free space.
  • The more the disks are used, the more fragmented they become, so the read/write head has to move to more locations to read all the parts of a file.
  • Fragmentation is the reason that files on the college's computers take a long time to open.

What defragmentation software does

  • It reorganises the blocks of each file so that they are stored together (contiguously) on the disk.
  • It collects the free space into one block so that new files are written in one piece and are less likely to be fragmented.
  • It is a housekeeping utility that is often supplied with the operating system, and it reorganises data that is already on the disk.
  • It does not change the contents of any file, it only changes where the blocks of the file are stored.

Benefits of running it

  • Files and programs open faster because the read/write head makes fewer movements, so the older computers feel quicker without the college buying new hardware.
  • Free space in one block means new files are written in one piece, so the improvement lasts for a while.
  • Running it may mean the college can keep using the older computers for longer instead of replacing them.

Drawbacks of running it

  • It can take a long time to run, so it should be scheduled for when the room is not in use, such as overnight or at weekends.
  • It causes a lot of disk activity, so running it too often puts unnecessary strain on the disks.
  • It does not free up any space, as no files are deleted, so the disks will still be almost full.
  • It only reorganises files that are intact, so it cannot recover a corrupted file, and a backup is still needed.

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 how files become fragmented and what defragmentation software does, with at least one benefit or drawback applied to the college's computers. An answer that only states what the software does and one benefit, with no explanation of how files became fragmented and no drawback, is Level 1 (2 marks).

Do not accept: defragmentation software compresses files, frees up storage space, deletes unused files, repairs corrupted files, or speeds up the processor or internet connection.

Example answers and how they were marked
Full marks6/6

As files are deleted and new ones saved, a file can be split into blocks in different places on the disk, especially a large file that will not fit into one free space. This means the read/write head has to move to more locations to read the file, which is why the files on these computers are slow to open. Defragmentation software reorganises the blocks so that each file is stored together, and it moves the free space into one block, so new files are written in one piece. Staff would find that files and programs open faster because the head makes fewer movements, so the older computers feel quicker without the college buying new ones. It can take a long time, so the college should schedule it overnight or at the weekend when the room is empty, and it should not be run too often because of the strain on the disks. It will not free up space, as nothing is deleted, so the disks will still be almost full and a backup is still needed.

Why: Level 3: fragmentation, the extra head movements and what the software does are explained accurately (AO1) and applied to the college's own computers, with a benefit and drawbacks including a sensible schedule (AO2).

Some marks2/6

Defragmentation software rearranges the files so that the parts of each file are stored together. This means files open faster, which will help on these computers. It should be run regularly.

Why: Level 1: two basic, independent points, namely that the software stores the parts of a file together and that files then open faster, with little linkage and no explanation of how the files became fragmented and no drawback, so Level 2 is not reached.

Some marks1/6

Defragmentation software compresses the files so they take up less space on the nearly full disks. If the parts of a file are stored together it opens faster.

Why: Level 1: only the basic point that storing the parts of a file together makes it open faster is creditworthy; the claim that defragmentation compresses files is a misconception on the do-not-accept line and is not credited.

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