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A word is a set number of bits managed as a unit.
Hardware Word
A hardware word is the group of bits normally managed by a processor. The word size is a distinguishing feature of a processor, and is typically a power-of-two multiple of eight bits (8, 16, 32, or 64 bits), although some rare or early processors used different word sizes.
The word size is usually associated with the size of general-purpose registers and the amount of data read from or written to memory at one time. Most modern processors can read/write alternate word sizes (for example, a "64-bit" x86_64 system can also read/write 32, 16, and 8 bit values to/from memory, and 64-bit registers can be accessed as 32, 16, or 8-bit subsets).
Common Names for Various Word Sizes
Bit
A bit is a single binary digit, a value that can take one of two states. These states may be referred to as:
- 1 or 0
- True or False
- On or Off (electrically)
Byte
A byte is a collection of eight bits. It is a convenient size for use with many small character sets such as [ASCII], [ISO8859], and EBCDIC], and can also be used with the [UTF-8] encoding of Unicode. It is often viewed as the smallest hardware word size that makes sense for general-purpose computing.
Most computers with larger hardware word sizes continue to rank memory, storage, and data sizes in bytes (or prefixed multiples of bytes) for comparability. For example, an x86_64 system will be advertised as having "16 gigabytes" of memory instead of "4 gigawords".
Octet
Another name for byte, commonly used in telecommunication standards and in French.
Nibble
A nibble (or nybble) is a half-byte, corresponding to one hexadecimal or BCD digit.