Data Storage Units

Data storage units are agreed sizes for describing how much data a computer can hold. They let you talk about a file or a drive in convenient amounts instead of counting individual bits.

Order of the units

From smallest to largest, the units are bit, nibble, byte, kilobyte (KB), megabyte (MB), gigabyte (GB), terabyte (TB) and petabyte (PB). A bit is the smallest unit of all; the nibble and byte are the next steps up before the amounts become much larger.

You choose the unit to suit the size. A short text document is measured in kilobytes, a photograph in megabytes, a film in gigabytes and a large data centre's storage in petabytes.

Steps of 1,000

From the kilobyte upwards, each unit is 1,000 times the size of the one before. The prefixes explain why: kilo means a thousand, mega a million, giga a thousand million and tera a million million, so every step multiplies by the same 1,000.

• A kilobyte is 1,000 bytes.
• A megabyte is 1,000 kilobytes.
• A gigabyte is 1,000 megabytes.
• A terabyte is 1,000 gigabytes.
• A petabyte is 1,000 terabytes.

The steps from bit to nibble and from nibble to byte are much smaller than 1,000, so those first three units do not fit the pattern.

You may also see each step from the kilobyte upwards given as 1,024 times the one before. That value is accepted too, but do not mix 1,000 and 1,024 within the same calculation.