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Edexcel 1CP2 · Topic 2 · 2.1e
Data
Units
Bits · Bytes · Kilobytes · Megabytes · Gigabytes · Terabytes
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Edexcel GCSE Computer Science 1CP2
Units of Data Storage
From Bits to Terabytes
Unit
Symbol
Size
Bit
b
Single binary digit (0 or 1)
Nibble
—
4 bits
Byte
B
8 bits
Kilobyte
KB
1,024 bytes
Megabyte
MB
1,024 KB
Gigabyte
GB
1,024 MB
Terabyte
TB
1,024 GB
Note: 1 KB = 1,024 bytes (not 1,000) because computers work in powers of 2 (2¹⁰ = 1,024)
Converting Between Units
Worked Examples
4 GB → MB: 4 × 1,024 =
4,096 MB
2,048 KB → MB: 2,048 ÷ 1,024 =
2 MB
0.5 GB → KB: 0.5 × 1,024 × 1,024 =
524,288 KB
Going up the scale: divide by 1,024 at each step
Going down the scale: multiply by 1,024 at each step
Real-World File Sizes
Putting Units in Context
A text document: ~50 KB
An MP3 music file: ~3–5 MB
A 4K video (1 hour): ~50–100 GB
A hard drive: 1–4 TB (most modern desktops)
Uncompressed image: width × height × colour depth (in bits) ÷ 8 = size in bytes
Exam Practice
Have a go at this question
Edexcel-style question
A USB drive has 16 GB of free space. A file of 500 MB is saved to the drive. How many megabytes of free space remain? Give your answer in GB.
3 marks
16 GB = 16 × 1,024 = 16,384 MB [1]. 16,384 − 500 = 15,884 MB remaining [1]. 15,884 ÷ 1,024 =
15.51 GB
(approx) [1].
Key Takeaways
What to Remember
1 byte = 8 bits; 1 nibble = 4 bits
Each step up ÷ 1,024; each step down × 1,024
Order: bit → nibble → byte → KB → MB → GB → TB
1 KB = 1,024 bytes (NOT 1,000) — computers use powers of 2