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The byte is a
unit of digital information
unit of digital information
that most commonly consists of eight
bit The bit is a basic unit of information in computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both ...
s. Historically, the byte was the number of bits used to encode a single
character Character(s) may refer to: Arts, entertainment, and media Literature * ''Character'' (novel), a 1936 Dutch novel by Ferdinand Bordewijk * ''Characters'' (Theophrastus), a classical Greek set of character sketches attributed to Theophrastus M ...
of text in a computer and for this reason it is the smallest addressable unit of
memory Memory is the faculty of the by which or is , stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If s could not be remembered, it would be impossible for language, r ...
in many
computer architecture In computer engineering Computer engineering (CoE or CpE) is a branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tun ...
s. To disambiguate arbitrarily sized bytes from the common
8-bit In computer architecture In computer engineering, computer architecture is a set of rules and methods that describe the functionality, organization, and implementation of computer systems. Some definitions of architecture define it as descr ...
definition,
network Network, networking and networked may refer to: Science and technology * Network theory Network theory is the study of Graph (discrete mathematics), graphs as a representation of either symmetric relations or directed graph, asymmetric relat ...
protocol documents such as The Internet Protocol (RFC 791)(1981) refer to an 8-bit byte as an
octet Octet may refer to: Music * Octet (music) In music, an octet is a musical ensemble consisting of eight Musical instrument, instruments or voices, or a musical composition written for such an ensemble. Octets in classical music Octets in Europea ...
. Those bits in an octet are usually counted with numbering from 0 to 7 or 7 to 0 depending on the
endianness In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softw ...
. The first bit is number 0, making the eighth bit number 7. The size of the byte has historically been
hardware Hardware may refer to: Technology Computing and electronics * Computer hardware, physical parts of a computer * Digital electronics, electronics that operate on digital signals * Electronic component, device in an electronic system used to affect e ...

hardware
-dependent and no definitive standards existed that mandated the size. Sizes from 1 to 48 bits have been used. The
six-bit character code A six-bit character code is a character encoding designed for use on computers with word lengths a multiple of 6. Six bits can only encode 64 distinct characters, so these codes generally include only the upper-case letters, the numerals, some punct ...
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. In this era, bit groupings in the instruction stream were often referred to as ''
syllables A syllable is a unit of organization for a sequence of Phone (phonetics), speech sounds. It is typically made up of a syllable nucleus (most often a vowel) with optional initial and final margins (typically, consonants). Syllables are often consid ...
'' or ''slab'', before the term ''byte'' became common. The modern
de facto standard A de facto standard is a custom or convention Convention may refer to: * Convention (norm), a custom or tradition, a standard of presentation or conduct ** Treaty, an agreement in international law * Convention (meeting), meeting of a (usually la ...
of eight bits, as documented in ISO/IEC 2382-1:1993, is a convenient
power of two Visualization of powers of two from 1 to 1024 (20 to 210) A power of two is a number of the form where is an integer An integer (from the Latin wikt:integer#Latin, ''integer'' meaning "whole") is colloquially defined as a number that can b ...
permitting the binary-encoded values 0 through 255 for one byte—2 to the power 8 is 256. The international standard
IEC 80000-13 ISO 80000 or IEC 80000 is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task which is applied to a common and repeate ...
codified this common meaning. Many types of applications use information representable in eight or fewer bits and processor designers optimize for this common 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. The unit symbol for the byte was designated as the upper-case letter B by the
International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French French (french: français(e), link=no) may refer to: * Something of, from, or related to France France (), officially the French Republic (french: link=no, République franç ...
(IEC) and
Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operations center in ...
(IEEE). Internationally, the unit ''
octet Octet may refer to: Music * Octet (music) In music, an octet is a musical ensemble consisting of eight Musical instrument, instruments or voices, or a musical composition written for such an ensemble. Octets in classical music Octets in Europea ...
'', symbol o, explicitly defines a sequence of eight bits, eliminating the ambiguity of the byte.


History

The term ''byte'' was coined by
Werner Buchholz Werner Buchholz (24 October 1922 – 11 July 2019) was a German-American computer scientist. After growing up in Europe, Buchholz moved to Canada and then to the United States. He worked for International Business Machines International Busin ...
in June 1956, during the early design phase for the IBM Stretch computer, which had addressing to the bit and variable field length (VFL) instructions with a byte size encoded in the instruction. It is a deliberate respelling of ''
bite A bite A bite is a wound received from the mouth of an animal or human; it is also a verb describing that action. Bite or BITE may also refer to: Related to biting * Biting, the process of chewing or mastication, whereby food is crushed and g ...

bite
'' to avoid accidental mutation to ''bit''. Another origin of ''byte'' for bit groups smaller than a computer's word size, and in particular groups of four bits, is on record by Louis G. Dooley, who claimed he coined the term while working with Jules Schwartz and Dick Beeler on an air defense system called SAGE at
MIT Lincoln Laboratory The MIT Lincoln Laboratory, located in Lexington, Massachusetts Lexington is a suburban town in Middlesex County, Massachusetts, United States. It is 11 miles (17 km) from Downtown Boston. The population was 31,394 at the 2010 census, whic ...
in 1956 or 1957, which was jointly developed by
Rand The RAND Corporation ("research and development") is an American nonprofit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and ope ...
, MIT, and IBM. Later on, Schwartz's language
JOVIAL Jovial may refer to: * Brice Jovial (born 1984), French football striker * JOVIAL, a programming language * Jovial High School, Yacharam, Telangana, India * Hamster Jovial, a French comic book series * The archaic adjectival form of: ** Jupiter ( ...
actually used the term, but the author recalled vaguely that it was derived from AN/FSQ-31. Early computers used a variety of four-bit
binary-coded decimal In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and soft ...
(BCD) representations and the six-bit codes for printable graphic patterns common in the
U.S. Army The United States Army (USA) is the land Land is the solid surface of the Earth that is not permanently covered by water. The vast majority of human activity throughout history has occurred in land areas that support agriculture ...
() and
Navy A navy, naval force, or maritime force is the branch of a nation's armed forces A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized a ...
. These representations included alphanumeric characters and special graphical symbols. These sets were expanded in 1963 to seven bits of coding, called the American Standard Code for Information Interchange (ASCII) as the
Federal Information Processing Standard The ' Federal Information Processing Standards (FIPS) are publicly announced developed by the for use in computer systems by non-military government agencies and government contractors. FIPS standards are issued to establish requirements for ...
, which replaced the incompatible teleprinter codes in use by different branches of the U.S. government and universities during the 1960s. ASCII included the distinction of upper- and lowercase alphabets and a set of
control character In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest comm ...
s to facilitate the transmission of written language as well as printing device functions, such as page advance and line feed, and the physical or logical control of data flow over the transmission media. During the early 1960s, while also active in ASCII standardization, IBM simultaneously introduced in its product line of
System/360 The IBM System/360 (S/360) is a family of mainframe computer systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover the complete range of applications, f ...
the eight-bit
Extended Binary Coded Decimal Interchange Code Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding six-b ...
(EBCDIC), an expansion of their
six-bit binary-coded decimal BCD ("Binary-Coded Decimal"), also called alphanumeric BCD, alphameric BCD, BCD Interchange Code, or BCDIC, is a family of representations of numerals, uppercase Latin letters, and some special and control characters as six-bit character code A si ...
(BCDIC) representations used in earlier card punches. The prominence of the System/360 led to the ubiquitous adoption of the eight-bit storage size, while in detail the EBCDIC and ASCII encoding schemes are different. In the early 1960s,
AT&T AT&T Inc. is an American multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, a s ...

AT&T
introduced
digital telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usual ...
on long-distance
trunk line In telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature o ...
s. These used the eight-bit μ-law encoding. This large investment promised to reduce transmission costs for eight-bit data. The development of eight-bit
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip ...

microprocessor
s in the 1970s popularized this storage size. Microprocessors such as the
Intel 8008 The Intel 8008 ("''eight-thousand-eight''" or "''eighty-oh-eight''") is an early byte-oriented microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, ...

Intel 8008
, the direct predecessor of the
8080 The Intel 8080 (''"eighty-eighty"'') is the second 8-bit In computer architecture, 8-bit integer An integer (from the Latin wikt:integer#Latin, ''integer'' meaning "whole") is colloquially defined as a number that can be written wi ...
and the
8086 The 8086 (also called iAPX 86) is a 16-bit 16-bit microcomputers are computers in which 16-bit microprocessors were the norm. A 16-bit register can store 216 different values. The range (computer programming), range of integer values that can b ...
, used in early personal computers, could also perform a small number of operations on the
four-bit In computer architecture In computer engineering, computer architecture is a set of rules and methods that describe the functionality, organization, and implementation of computer systems. Some definitions of architecture define it as d ...
pairs in a byte, such as the decimal-add-adjust (DAA) instruction. A four-bit quantity is often called a
nibble In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest c ...
, also ''nybble'', which is conveniently represented by a single
hexadecimal In and , the hexadecimal (also base 16 or hex) numeral system is a that represents numbers using a (base) of 16. Unlike the system representing numbers using 10 symbols, hexadecimal uses 16 distinct symbols, most often the symbols "0"–"9 ...
digit. The term ''
octet Octet may refer to: Music * Octet (music) In music, an octet is a musical ensemble consisting of eight Musical instrument, instruments or voices, or a musical composition written for such an ensemble. Octets in classical music Octets in Europea ...
'' is used to unambiguously specify a size of eight bits. It is used extensively in
protocol Protocol may refer to: Sociology and politics * Protocol (politics) Protocol originally (in Late Middle English, c. 15th century) meant the minutes or logbook taken at a meeting, upon which an agreement was based. The term now commonly refers to a ...
definitions. Historically, the term ''octad'' or ''octade'' was used to denote eight bits as well at least in Western Europe; however, this usage is no longer common. The exact origin of the term is unclear, but it can be found in British, Dutch, and German sources of the 1960s and 1970s, and throughout the documentation of
Philips Koninklijke Philips N.V. (in Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () *Dutch language , spoken in Belgium (also referred as ''flemish'') Dutch may also refer t ...

Philips
mainframe computers.


Unit symbol

The unit symbol for the byte is specified in
IEC 80000-13 ISO 80000 or IEC 80000 is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task which is applied to a common and repeate ...
,
IEEE 1541 IEEE 1541-2002 is a standard issued in 2002 by the Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a professional association for electronic engineering and electrical engineering ...
and the Metric Interchange Format as the upper-case character B. In the
International System of Quantities The International System of Quantities (ISQ) consists of the quantities Quantity is a property that can exist as a Counting, multitude or Magnitude (mathematics), magnitude, which illustrate discontinuity (mathematics), discontinuity and continu ...
(ISQ), B is the symbol of the '' bel'', a unit of logarithmic power ratio named after
Alexander Graham Bell Alexander Graham Bell (; March 3, 1847 – August 2, 1922) was a Scottish-born inventor, scientist, and engineer who is credited with inventing and patenting the first practical telephone. He also co-founded the (AT&T) in 1885. , grandf ...

Alexander Graham Bell
, creating a conflict with the IEC specification. However, little danger of confusion exists, because the bel is a rarely used unit. It is used primarily in its decadic fraction, the
decibel The decibel (symbol: dB) is a relative equal to one tenth of a bel (B). It expresses the ratio of two values of a on a . Two signals whose differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 10 (approxim ...

decibel
(dB), for
signal strength In telecommunications Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of ...
and
sound pressure level Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrop ...
measurements, while a unit for one-tenth of a byte, the decibyte, and other fractions, are only used in derived units, such as transmission rates. The lowercase letter o for
octet Octet may refer to: Music * Octet (music) In music, an octet is a musical ensemble consisting of eight Musical instrument, instruments or voices, or a musical composition written for such an ensemble. Octets in classical music Octets in Europea ...
is defined as the symbol for octet in IEC 80000-13 and is commonly used in languages such as and
Romanian Romanian may refer to: *anything of, from, or related to the country and nation of Romania Romania ( ; ro, România ) is a country at the crossroads of Central Europe, Central, Eastern Europe, Eastern and Southeast Europe, Southeastern Euro ...
, and is also combined with metric prefixes for multiples, for example ko and Mo. The usage of the term ''octad(e)'' for eight bits is no longer common.


Multiple-byte units

More than one system exists to define larger units based on the byte. Some systems are based on
powers of 10A power of 10 is any of the integer powers of the number ten; in other words, ten multiplied by itself a certain number of times. Power of 10, Power of ten, or Powers of Ten may refer to: *Power of 10 (American game show), ''Power of 10'' (American ...
; other systems are based on . Nomenclature for these systems has been the subject of confusion. Systems based on powers of 10 reliably use standard
SI prefix The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms_and_initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wi ...
es ('
kilo KILO (94.3 FM, 94.3 KILO) is a radio station broadcasting in Colorado Springs The City of Colorado Springs is the List of cities and towns in Colorado#Home rule municipality, Home Rule Municipality that is the county seat and the List of ci ...
', '
mega Mega or MEGA may refer to: Science * mega-, the SI prefix for one million (106, symbol M) * Mega (number), a certain very large integer in Steinhaus–Moser notation * "mega-" a prefix meaning "large" that is List of commonly used taxonomic affi ...
', '
giga Giga ( or ) is a unit prefixA unit prefix is a specifier or mnemonic that is prepended to units of measurement to indicate multiples or fractions of the units. Units of various order of magnitude, sizes are commonly formed by the use of such prefi ...
', ...) and their corresponding symbols (k, M, G, ...). Systems based on powers of 2, however, might use
binary prefix A binary prefix is a unit prefix for multiples of Units of measurement, units in data processing, data transmission, and digital information, notably the bit and the byte, to indicate multiplication by a Exponentiation, power of 2. The comput ...
es ('kibi', 'mebi', 'gibi, ...) and their corresponding symbols (Ki, Mi, Gi, ...) ''or'' they might use the prefixes K, M, and G, creating ambiguity. While the numerical difference between the decimal and binary interpretations is relatively small for the kilobyte (about 2% smaller than the kibibyte), the systems deviate significantly as units grow larger (the relative deviation grows by 2.4% for each three orders of magnitude). For example, a power-of-10-based yottabyte is about 17% smaller than power-of-2-based yobibyte.


Units based on powers of 10

Definition of prefixes using powers of 10—in which 1 ''kilobyte'' (symbol kB) is defined to equal 1000 bytes—is recommended by the
International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French French (french: français(e), link=no) may refer to: * Something of, from, or related to France France (), officially the French Republic (french: link=no, République franç ...
(IEC).Prefixes for Binary Multiples
— The NIST Reference on Constants, Units, and Uncertainty
The IEC standard defines eight such multiples, up to 1 yottabyte (YB), equal to 10008 bytes. This definition is most commonly used for data transfer rates in
computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are made up of technologies, based on physically wired, optical, and wire ...
s, internal bus, hard drive and flash media transfer speeds, and for the capacities of most
storage media On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage equipment and the magnetic tape is a data storage medium. Data Data are units of information Information can be thought of as the resolution of uncertaint ...
, particularly
hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage equipment and the magnetic tape is a data storag ...
s,
flash FLASH, acronym of ''Free Electron LASer in Hamburg'', a particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it was the ...
-based storage, and
DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electr ...

DVD
s. It is also consistent with the other uses of the
SI prefix The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms_and_initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wi ...
es in computing, such as or .


Units based on powers of 2

A system of units based on in which 1 kibibyte (KiB) is equal to 1024 (i.e., 210) bytes is defined by international standards IEC 80000-13 and supported by national and international standards bodies (
BIPM The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental organisation, through which its 59 member-states act together on measurement standards in four areas: chemistry, ...

BIPM
, IEC,
NIST The National Institute of Standards and Technology (NIST) is a physical sciences Physical science is a branch of natural science that studies abiotic component, non-living systems, in contrast to life science. It in turn has many branches, e ...

NIST
). The IEC standard defines eight such multiples, up to 1 yobibyte (YiB), equal to 10248 bytes. An alternate system of nomenclature for the same units, in which 1 ''kilobyte'' (KB) is equal to 1024 bytes, 1 ''megabyte'' (MB) is equal to 10242 bytes and 1 ''gigabyte'' (GB) is equal to 10243 bytes is defined by a 1990s
JEDEC The JEDEC Solid State Technology Association is an independent semiconductor engineering trade organization and standardization body headquartered in Arlington County, Virginia Arlington County is a county A county is a geographical re ...
standard. Only the first three multiples (up to GB) are defined by the JEDEC standard. For TB and larger, standards recognise only the decimal definition. The JEDEC convention is prominently used by the
Microsoft Windows Microsoft Windows, commonly referred to as Windows, is a group of several proprietary {{Short pages monitor