Units of
Information

Bits · Nibbles · Bytes · KB · MB · GB · TB

CSZoneAQA GCSE Computer Science 8525

Units of Data Storage

From Bits to Terabytes

Unit	Abbreviation	Size
Bit	b	Smallest unit — stores a 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

Why 1,024 and not 1,000?

Binary and Powers of 2

Computers work in binary, so storage is measured in powers of 2. 1 KB = 2¹⁰ = 1,024 bytes (not 1,000). This is different from the metric system (1 km = 1,000 m).

1 KB = 1,024 B = 2¹⁰ bytes
1 MB = 1,024 KB = 2²⁰ bytes ≈ 1 million bytes
1 GB = 1,024 MB = 2³⁰ bytes ≈ 1 billion bytes
1 TB = 1,024 GB = 2⁴⁰ bytes ≈ 1 trillion bytes

Real-World File Sizes

Typical Data Sizes

A plain text file (this sentence): ~50 bytes

A small webpage: ~100 KB

A high-quality photo (JPEG): ~3–5 MB

A 3-minute MP3 song: ~3–4 MB

A 2-hour 4K film: ~50–80 GB

Exam tip:You may need to calculate file sizes — practice converting between KB, MB, GB.

Exam Practice

Have a go at this question

AQA-style question

A sound file has a size of 4,096 KB. Express this in:
(a) MB (b) GB

2 marks

(a) 4,096 ÷ 1,024 = 4 MB [1]
(b) 4 ÷ 1,024 = 0.00390625 GB (≈ 0.004 GB) [1]

Key Takeaways

What to Remember

Bit = 0 or 1 · Nibble = 4 bits · Byte = 8 bits

Each step ×1024: B → KB → MB → GB → TB

1,024 not 1,000 because computers use binary (powers of 2)

To convert down (to smaller unit): multiply × 1,024. To convert up: divide ÷ 1,024