gcsecomputerscience.co.uk
Data Efficiency 0 / 16
Compression Rank Bloated Block
1 [5 Marks Total]
(a) State two benefits of compressing a file. [2]
(b) Identify whether each statement applies to Lossy or Lossless compression. [3]
Original file can be perfectly reconstructed
Data is permanently removed
Usually creates much smaller file size
✅ Mark Scheme

(a) Benefits: Reduces file size, Faster transmission/download, Uses less bandwidth.

(b) Table:

  • Perfectly reconstructed -> Lossless
  • Permanently removed -> Lossy
  • Much smaller size -> Lossy
Score yourself (Max 5):
2 [3 Marks Total]
A student is emailing a Python program code file.
(a) Which compression type must they use? [1]
(b) Explain why the other type is unsuitable. [2]
✅ Mark Scheme

(a) Lossless

(b) Explanation:

  • Lossy permanently removes data (1).
  • If code text is removed, the program will crash/error (1).
Score yourself (Max 3):
3 [4 Marks Total]
A web designer uses Lossy compression for website images.
(a) Explain one reason why Lossy is better for websites. [2] (b) Explain one negative effect on the image. [2]
✅ Mark Scheme

(a) Reason: File size is significantly smaller (1), so the page loads faster (1).

(b) Effect: Quality reduces (1), image may look pixelated/blurry (1).

Score yourself (Max 4):
4 [4 Marks Total]
Explain the fundamental difference between Lossy and Lossless compression regarding file restoration.
✅ Mark Scheme
  • Lossy: Permanently removes data, cannot restore original (1).
  • Lossless: Retains all data, restores file to exact original state (1).
  • Comparison: Lossy = smaller but lower quality vs Lossless = larger but perfect quality (1).
Score yourself (Max 4):