Bit, Nibble, Byte, KB, MB, GB, TB, PB

The units of data storage: Bit, Nibble, Byte, KB, MB, GB, TB, PB

1.2.3 Units

Units — Note 1 of 3

What you need to know

Data in computers is measured in specific units, from the smallest (bit) to the largest (petabyte). Understanding these units and being able to convert between them is fundamental to Computer Science.

What to know

1 Kilobyte (KB) = 1,000 bytes. 1 Megabyte (MB) = 1,000 KB. 1 Gigabyte (GB) = 1,000 MB. 1 Terabyte (TB) = 1,000 GB. 1 Petabyte (PB) = 1,000 TB.

Key terms

Bit: The smallest unit of data, a single binary digit (0 or 1).
Nibble: 4 bits (half a byte).
Byte: 8 bits.

Exam technique

Tip:The OCR specification uses DECIMAL prefixes (multiply by 1,000). Using 1,024 is also acceptable but 1,000 is the default.
Mistake:Confusing bits and bytes. There are 8 bits in 1 byte. File sizes are usually given in bytes; data transfer speeds are often in bits per second.
Tip:When comparing file sizes, convert ALL to the SAME unit first. E.g. to compare 2.1 GB, 300 MB, 200,000 KB and 0.0021 TB, convert all to MB or KB.

Example:2000 bytes = 2 kilobytes. 2000 terabytes = 2 petabytes. 16 bits = 2 bytes. 4 nibbles = 2 bytes.

Ready to test yourself?

Practise 1.2.3 questions

← Previous topicCapacity, speed, portability, durability, reliability, cost1.2.2 Secondary Storage Next note →How data needs to be converted into a binary format to be processed by a computer1.2.3 Units

Back to Units

Revise another OCR GCSE topic: Data Storage: Numbers