Units of Memory

A computer system stores and processes everything using binary numbers — sequences of the digits 0 and 1. The units in which memory is measured are therefore built up from the binary digit itself.

Bit, nibble and byte

• Bit — the binary digits 0 and 1 are the basic units of memory; each single 0 or 1 is one bit.
• Word — bits are grouped together to form words.
• Nibble — a 4-bit word is called a nibble. Examples: 1001, 1010, 0010.
• Byte — a two-nibble word, i.e. an 8-bit word, is called a byte. Examples: 01000110, 01111100, 10000001.

The byte is the standard building block: like any other standard unit, bytes are grouped together into bigger chunks of memory.

The ladder of memory units

Table 1.1 gives the measurement units for digital data stored in storage devices. Each unit is 1024 times the one before it:

So the full chain runs: bit → nibble (4 bits) → byte (8 bits) → KB → MB → GB → TB → PB → EB → ZB → YB, with a factor of 1024 at every step from bytes upward. …