Explain why data is compressed
Connect smaller files to lower storage use, bandwidth and transmission time while respecting data-quality needs.
This sequence follows Cambridge IGCSE Computer Science 0478, 2026–2028 syllabus Version 6. It covers subject content sections 1.1–1.3 only. The separately published 2029–2031 syllabus is not mapped here. Practice is original, self-checked and does not award an official Cambridge grade. Full timed papers and human subject-teacher review remain outstanding.
Before you begin
- No programming language is required. Be comfortable with place value and multiplication; each lesson introduces the computer-science notation it uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the purpose of file compression?
What you will learn
- Explain the purpose of compression
- Link reduced file size to storage and transmission benefits
- Choose compression based on how the data will be used
Smaller files are easier to store and send
Compression reduces the amount of data needed to represent a file. A smaller file uses less storage, requires less bandwidth and can take less time to transmit.
Apply and check the rule
The appropriate method depends on the file and its use. If every original value must be recovered, use a lossless method. If small quality changes are acceptable, lossy compression may achieve a smaller file.
Pause and explain
A file must be transferred over a slow connection. What is one likely benefit of compression?
Worked example
A school stores thousands of unchanged archive scans and also streams music. Why might their compression choices differ?
Show the worked solution
- Archives may need exact recovery, so lossless compression protects every original value.
- Streaming benefits from smaller files and may accept a controlled quality reduction.
- The best choice depends on the purpose and acceptable loss.
Answer Use lossless compression for exact archival recovery; lossy compression may suit streaming where a smaller file is more important than perfect reconstruction.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain why a compressed file can reduce network costs.
Give me a hint
Connect file size to bandwidth and time.
Compare my reasoning
- The compressed file contains fewer bits to transfer.
- It uses less bandwidth for the same transfer and can take less time.
- Lower transfer volume may reduce network usage costs.
A smaller file needs less bandwidth and time to send, which can reduce network usage costs.
Look for these in your work
- Fewer bits stated
- Bandwidth/time link
- Cost implication explained
A laboratory must retain exact numeric measurements for later reanalysis. What property should its compression method have?
Give me a hint
Consider whether the original values may need to be recovered exactly.
Compare my reasoning
- The method should preserve every original value.
- Lossless compression permits exact reconstruction.
- This avoids changing the measurements used in later analysis.
Use lossless compression so the original measurements can be recovered exactly.
Look for these in your work
- Exactness requirement
- Lossless method selected
- Reason stated
A video platform is deciding whether to reduce file sizes aggressively. Explain the storage/network benefit and a possible user-facing cost.
Give me a hint
Evaluate both transfer benefits and fidelity.
Compare my reasoning
- Smaller files use less server storage.
- They require less bandwidth and may stream faster.
- Aggressive lossy compression can remove detail and reduce image or sound quality.
Aggressive compression can reduce storage and bandwidth use and speed delivery, but lossy compression may visibly or audibly reduce quality.
Look for these in your work
- Storage benefit
- Network benefit
- Quality cost
Common mistakes
- Saying compression always improves quality
- Choosing a method based only on file size and ignoring the need to recover the original
What can you explain now?
Name two benefits of a smaller compressed file.
Compare with the explanation
It uses less storage and needs less bandwidth or transmission time
Reduced size benefits both storage and transfer.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Which two resource limits are reduced when compression makes a file smaller?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.