Byte

This article is about the unit of information. For other uses, see Byte (disambiguation).
byte
Unit systemunit derived from bit
Unit ofdigital information, data size
SymbolB, o (when 8 bits)

The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer[1][2] and for this reason it is the smallest addressable unit of memory in many computer architectures. To disambiguate arbitrarily sized bytes from the common 8-bit definition, network protocol documents such as the Internet Protocol (RFC 791) refer to an 8-bit byte as an octet.[3] Those bits in an octet are usually counted with numbering from 0 to 7 or 7 to 0 depending on the bit endianness.

The size of the byte has historically been hardware-dependent and no definitive standards existed that mandated the size. Sizes from 1 to 48 bits have been used.[4][5][6][7] The six-bit character code 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 memory words 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 syllables[a] or slab, before the term byte became common.

The modern de facto standard of eight bits, as documented in ISO/IEC 2382-1:1993, is a convenient power of two permitting the binary-encoded values 0 through 255 for one byte, as 2 to the power of 8 is 256.[8] The international standard IEC 80000-13 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.[9] 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 International Electrotechnical Commission (IEC) and Institute of Electrical and Electronics Engineers (IEEE).[10] Internationally, the unit octet explicitly defines a sequence of eight bits, eliminating the potential ambiguity of the term "byte".[11][12] The symbol for octet, 'o', also conveniently eliminates the ambiguity in the symbol 'B' between byte and bel.

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  2. ^ Cite error: The named reference Bemer_1959 was invoked but never defined (see the help page).
  3. ^ Postel, J. (September 1981). Internet Protocol DARPA INTERNET PROGRAM PROTOCOL SPECIFICATION. p. 43. doi:10.17487/RFC0791. RFC 791. Retrieved 28 August 2020. octet An eight bit byte.
  4. ^ Cite error: The named reference Buchholz_1956_1 was invoked but never defined (see the help page).
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  8. ^ Cite error: The named reference ISO_IEC_2382-1_1993 was invoked but never defined (see the help page).
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  11. ^ Cite error: The named reference TCPIP was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference ISO_2382-4 was invoked but never defined (see the help page).


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