Byte

The byte is a <a href="/facts/Units_of_information/lxjSrVJM">unit of digital information</a> that most commonly consists of eight <a href="/facts/Bit/RwfjaYSv">bits</a>. Historically, the byte was the number of bits used to encode a single <a href="/facts/Character_(computing)/X2zKLFFB">character</a> of text in a computer and for this reason it is the smallest <a href="/facts/Address_space/EscyYKkP">addressable</a> unit of <a href="/facts/Computer_memory/hQKVQ51J">memory</a> in many <a href="/facts/Computer_architecture/tHtwxgR2">computer architectures</a>. To disambiguate arbitrarily sized bytes from the common <a href="/facts/8-bit_computing/2CkhLNoH">8-bit</a> definition, <a href="/facts/Computer_network/3w5RM99p">network</a> protocol documents such as the <a href="/facts/Internet_Protocol/Qq6VeEal">Internet Protocol</a> (<a href="/facts/RFC_(identifier)/esftTvE7">RFC</a> <a href="https://www.rfc-editor.org/rfc/rfc791">791</a>) refer to an 8-bit byte as an <a href="/facts/Octet_(computing)/dqCHsuUF">octet</a>. Those bits in an octet are usually counted with numbering from 0 to 7 or 7 to 0 depending on the <a href="/facts/Bit_numbering/94h4P3qr">bit endianness</a>.
The size of the byte has historically been <a href="/facts/Computer_hardware/8jSjsCNv">hardware</a>-dependent and no definitive standards existed that mandated the size. Sizes from 1 to 48 bits have been used. The <a href="/facts/Six-bit_character_code/98y42p1u">six-bit character code</a> was an often-used implementation in early encoding systems, and computers using six-bit and nine-bit bytes were common in the 1960s. These systems often had <a href="/facts/Word_(computer_architecture)/2e5umRaj">memory words</a> of 12, 18, 24, 30, 36, 48, or 60 bits, corresponding to 2, 3, 4, 5, 6, 8, or 10 six-bit bytes, and persisted, in legacy systems, into the twenty-first century. In this era, bit groupings in the instruction stream were often referred to as <a href="/facts/Syllable_(computing)/9sQACN4o">syllables</a> or slab, before the term byte became common.
The modern <a href="/facts/De_facto_standard/TRELHVwI">de facto standard</a> of eight bits, as documented in ISO/IEC 2382-1:1993, is a convenient <a href="/facts/Power_of_two/MA6WEpTt">power of two</a> permitting the <a href="/facts/Binary_number/a6JDSRPs">binary-encoded</a> values 0 through 255 for one byte, as 2 to the power of 8 is 256. The international standard <a href="/facts/IEC_80000-13/k1nrIjMW">IEC 80000-13</a> codified this common meaning. Many types of applications use information representable in eight or fewer bits and processor designers commonly optimize for this usage. The popularity of major commercial computing architectures has aided in the ubiquitous acceptance of the 8-bit byte. Modern architectures typically use 32- or 64-bit words, built of four or eight bytes, respectively.
The unit symbol for the byte was designated as the upper-case letter B by the <a href="/facts/International_Electrotechnical_Commission/hSK0kjwI">International Electrotechnical Commission</a> (IEC) and <a href="/facts/Institute_of_Electrical_and_Electronics_Engineers/UddC4pUW">Institute of Electrical and Electronics Engineers</a> (IEEE). Internationally, the unit <a href="/facts/Octet_(computing)/dqCHsuUF">octet</a> explicitly defines a sequence of eight bits, eliminating the potential ambiguity of the term "byte". The symbol for octet, 'o', also conveniently eliminates the ambiguity in the symbol 'B' between byte and <a href="/facts/Decibel/0LyxAPXh">bel</a>.

Byte open-in-new

Byte