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Edexcel GCSE Computer Science (1CP2) Exam Questions

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3 questions · 5 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 recall1 markCompression Swap Remove

A company backs up its files to an external hard drive.

Give one reason why the company compresses the files before backing them up.

[1 mark]
Mark scheme

Award one mark for any of the following:

  • More files/data can be stored (in the same storage space) (1)
  • The files take up less storage space (1)
  • The backup is quicker/faster to complete (1)
  • Less data needs to be transferred to the backup device (1)

Do not accept 'makes the files more secure' or 'encrypts the files'.

Example answers and how they were marked
Full marks1/1

The compressed files take up less storage space, so more files can be backed up.

Why: The files take up less storage space (1).

No marks0/1

It reduces the amount of disk fragmentation.

Why: Near-miss: compression does not reduce disk fragmentation.

No marks0/1

It encrypts the files so they are safer if the drive is stolen.

Why: Misconception: compression does not encrypt files, and security is not accepted.

3Explain2 marksCompression Swap Remove

A text file contains the same phrase many times.

Explain how lossless compression can reduce the size of this text file.

[2 marks]
Mark scheme

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

  • The repeated phrase is stored once (1) along with a count of the number of times it occurs (1)
  • The repeated phrase is replaced by a shorter code/reference (1) and the original phrase is held in a dictionary/lookup table (1)
  • A shorter code is used in place of each repeated phrase (1) so fewer characters/bits are needed to store the file (1)
  • Groups of repeated characters are replaced by a count and a single value (1) so the file stores less data (1)

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

Allow naming of a suitable method, e.g. run-length encoding or dictionary coding, in place of a description of that method.

Award the marks once only where the same method (run-length encoding) is described more than once.

Do not accept 'it makes the file smaller' on its own without a method of compression.

Do not accept answers that describe lossy compression, e.g. that data/detail is removed or lost permanently, because lossless compression keeps all of the original data.

Do not accept 'it removes the repeated words/duplicates' on its own, as this suggests data is lost; credit only where the answer says the phrase is stored once with a count or code.

Example answers and how they were marked
Full marks2/2

The repeated phrase is stored once and a count of how many times it occurs is stored with it.

Why: Phrase stored once (1) with the linked reason that a count of the repeats is also stored (1).

Some marks1/2

It finds the repeated patterns in the text and replaces them with a shorter code.

Why: Shorter code used in place of the repeated phrase (1) but no linked reason about fewer characters/bits being stored.

No marks0/2

It permanently removes the repeated words so there is less data to store.

Why: Describes lossy compression; the Do not accept line rejects removal of data because lossless compression keeps all of the original data.

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 16 questions Intellectual Property 12 questions

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