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Year 9

File size and compression

I can explore what compression is and the impact it can have on the size and quality of a file.

icon-background-square
New
New
Year 9

File size and compression

I can explore what compression is and the impact it can have on the size and quality of a file.

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Lesson details

Key learning points

  1. Compression is used to reduce the size of digital files.
  2. Lossy and lossless compression affects digital files.
  3. Using compressed files has both benefits and drawbacks for the use and transfer of file.

Keywords

  • Lossy compression - a method where data is permanently lost during the compression process and must be approximated when the file is decompressed

  • Lossless compression - a method of compression where no data is permanently lost during the process

Common misconception

Compression always reduces quality or that compressed files are always lower quality than uncompressed files.

Lossless compression retains all original data by finding and storing repeated patterns more efficiently.


To help you plan your year 9 computing lesson on: File size and compression, download all teaching resources for free and adapt to suit your pupils' needs...

Just as abbreviating common words saves space in writing, compression algorithms find repetitive patterns in data and replaces them with shorter codes. This reduces file size without losing the essential information.
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This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
What is the smallest unit of data in a computer system?
Correct Answer: bit, a bit
Q2.
What is the term for the number of pixels in an image?
Correct Answer: resolution
Q3.
What happens when you increase the resolution of an image?
the file size decreases
Correct answer: the image quality improves
the image becomes monochrome
the colours change
Q4.
What does colour depth refer to?
Correct answer: the number of bits used to represent a colour
the brightness of an image
the number of colours in an image
the size of an image
Q5.
What is the effect of using a higher sample resolution for sound files?
lower quality
smaller file size
Correct answer: more accurate sound representation
fewer sound channels
Q6.
How does the size of a file affect its transfer speed over a network?
file size does not affect transfer speed
larger files always transfer at the same speed as smaller files
larger files transfer faster than smaller files
Correct answer: larger files transfer slower than smaller files

6 Questions

Q1.
What type of compression permanently removes data?
Correct Answer: lossy, Lossy compression
Q2.
What is the term for compression that retains all original data?
Correct Answer: lossless, Lossless compression
Q3.
Match the terms with their definitions.
Correct Answer:compression,reducing file size
tick

reducing file size

Correct Answer:decompression,restoring file to original size
tick

restoring file to original size

Correct Answer:lossy compression,permanently removes data
tick

permanently removes data

Correct Answer:lossless compression,retains all original data
tick

retains all original data

Correct Answer:file size,the amount of data a file contains
tick

the amount of data a file contains

Q4.
Which compression method is typically used for audio and video files to save space?
Correct answer: lossy
lossless
temporary
permanent
Q5.
How does compression affect file transfer speeds?
it slows them down
Correct answer: it speeds them up
it has no effect
it makes them unpredictable
Q6.
What is a key feature of lossless compression?
it reduces quality
it increases file size
Correct answer: it retains all original data without quality loss
it permanently removes data