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Edexcel GCSE Computer Science (1CP2) Exam Questions

Build a practice paper from 693 exam-style questions, each with its mark scheme and example answers. Print it, or answer it on paper and then open the mark schemes. Or browse the questions by topic.

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3 questions · 6 marks

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1Short 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 any 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.

2Short recall2 marksUnits & Conversion Swap Remove

A solid state drive has a capacity of 5 gibibytes.

Give an expression to calculate the number of bits in 5 gibibytes. You do not need to do the calculation.

[2 marks]
Mark scheme

Award one mark for each of:

  • 5 × 1024^3 / 5 × 1024 × 1024 × 1024 / 5 × 2^30, for the number of bytes (1)
  • A fully correct expression with × 8 to convert bytes to bits, in any order, e.g. 5 × 1024^3 × 8, 8 × 5 × 2^30 (1)

Accept 5 × 1 073 741 824 × 8.

Accept 5 × 2^33 or 42 949 672 960 as a fully correct expression (2 marks).

Do not accept 5 × 1000^3 × 8, which uses decimal multiples.

Do not accept ÷ 8, which converts bits to bytes.

Example answers and how they were marked
Full marks2/2

8 × 5 × 2^30

Why: 5 × 2^30 is the number of bytes (1) and × 8 converts bytes to bits (1).

Some marks1/2

5 × 2^30

Why: Correct number of bytes using the binary multiple 2^30 (1), but no conversion to bits.

No marks0/2

5 × 1000^3 × 8

Why: Uses decimal 1000^3 instead of binary 1024^3, so the expression is not fully correct; no creditworthy point.

3Describe2 marksCompression Swap Remove

Photographs are often saved as JPG files.

Describe how lossy compression reduces the size of a photograph.

[2 marks]
Mark scheme

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

  • Some data is removed permanently (1) choosing detail that people are least likely to notice (1)
  • Small changes in colour/shade are discarded (1) so fewer different values need to be stored (1)
  • Similar pixels are stored as one value (1) so there are fewer values in the file (1)
  • Fine detail is removed (1) so fewer bits are needed to store each area (1)

Do not accept answers that say repeated patterns are stored once / no data is lost.

Example answers and how they were marked
Full marks2/2

It permanently removes some of the pixel data that the human eye is unlikely to notice, such as small colour changes.

Why: Linked point: data removed permanently (1) and development: detail least noticeable (1).

Some marks1/2

Some of the data in the photograph is removed permanently.

Why: States permanent removal of data (1); no linked development is given (1).

No marks0/2

It finds repeated pixels and stores them once, so no data is lost.

Why: Describes lossless compression, not lossy; no credit.

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