Units and file sizes for GCSE Computer Science
GCSE Computer Science, Data. Usually met in years 9 to 11.
Work with bits, bytes, kilobytes and megabytes, and calculate the size of image and sound files.
What you practise
- Converting between units
- Image file size from width, height and colour depth
- Sound file size from sample rate, bit depth and length
Starts with bits in a byte and builds to sound file sizes. Practice moves up a level when a round goes well and down when it does not.
Sample questions
Each sample comes with the method and the reason every wrong option is wrong. Real practice rounds are ten questions at your level.
Sample question, level 2 of 5
How many bytes are in 6 kilobytes? Use 1 KB = 1000 bytes.
- 600
- 6,144
- 0.006
- 6,000
- 48
Show the answer and method
Answer: D, 6,000
The method: 1 KB = 1000 bytes, so 6 KB = 6,000 bytes.
Why the other options are wrong:
- A, 600: There are 1000 bytes in a KB, not 100.
- B, 6,144: That uses 1024 bytes, which is a kibibyte (KiB). A kilobyte is 1000 bytes.
- C, 0.006: That divides. Kilobytes are bigger, so there are more bytes.
- E, 48: That multiplies by 8, as for bits in a byte.
Sample question, level 4 of 5
An image uses 32 different colours. What is the smallest colour depth it needs, in bits?
- 6
- 5
- 32
- 4
- 16
Show the answer and method
Answer: B, 5
The method: 2 to the power 5 = 32, so 5 bits are enough for 32 colours.
Why the other options are wrong:
- A, 6: 5 bits already give 32 colours.
- C, 32: That is the number of colours, not bits.
- D, 4: 4 bits give only 16 colours.
- E, 16: That halves the number of colours. Find the power of 2 instead.
See where this fits: every GCSE option topic and Key Stage 3.
Related topics: Binary, Hexadecimal.
