[[Category:Computer Architecture]]{{Chris Tyler Draft}} A word is a set number of bits managed as a unit. 

A ''hardware word'' is the group of bits normally managed by a processor. This 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 [[Register|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). Additionally, many modern systems use a different memory word size than CPU word size (for example, a "64-bit" system may be built to read/write memory 128 bits at a time), but this is transparent to the programmer and user. == 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)* Positive or Negative charge, or Forward or Reverse current flow (electrically - differential signalling) === Byte === A byte is a collection of eight '''bits'''. It is a convenient size for use with many small character sets such as [http://czyborra.com/charsets/iso646.html ASCII], [http://czyborra.com/charsets/iso8859.html ISO8859], and [http://czyborra.com/charsets/iso646.html#EBCDIC EBCDIC], and can also be used with the [http://czyborra.com/utf/#UTF-8 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 "2 gigawords". === Octet === Another name for [[#Byte|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. === Half word, Single word, Double word, Quad word === The terms half word (or halfword or half-word), single word, double word, and quad word are often used in contemporary computing to refer to common word sizes relative to a 32-bit base word size:* half word = 16 bits* single word = 32 bits* double word = 64 bits* quad word = 128 bits This terminology can be seen, for example, in the lane naming conventions for AArch64 SIMD (where <code>v0.8h</code> refers to the 128-bit vector register 0 divided in eight half word lanes) and x86_86 instruction suffixes (MOVQ to move a quad word).

The word 32-bit base size is usually associated with reflective of the register 32-bit standard integer size used in the predominant LP64 (and the amount of data read/written from/to memory at one timeless common ILP32) programming models.