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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 Music is the art of arranging sounds in time to produce a composition through the elements of melody, harmony, rhythm, and timbre. It is one of the universal cultural Culture () is ...
. 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 that has achieved a dominant position by public acceptance or market forces (for example, by early entrance to the market). is a Latin phrase that means ''in fact'' (literally by or from fact) in th ...
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 Music is the art of arranging sounds in time to produce a composition through the elements of melody, harmony, rhythm, and timbre. It is one of the universal cultural Culture () is ...
'', 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 JOVIAL is a high-level programming language In computer science Computer science deals with the theoretical foundations of information, algorithms and the a ...
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
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() and
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. 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 A pair of IBM mainframes. On the left is the IBM z Systems z13. On the right is the IBM LinuxONE Rockhopper.">IBM_LinuxONE.html" ;"title="IBM z Systems z13. On the right is the ...
the eight-bit
Extended Binary Coded Decimal Interchange Code Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an 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 t ...
(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,
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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, also ''nybble'', which is conveniently represented by a single hexadecimal digit. The term ''
octet Octet may refer to: Music * Octet (music) In music Music is the art of arranging sounds in time to produce a composition through the elements of melody, harmony, rhythm, and timbre. It is one of the universal cultural Culture () is ...
'' is used to unambiguously specify a size of eight bits. It is used extensively in Protocol (computing), protocol 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 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 and the Metric Interchange Format as the upper-case character B. In the International System of Quantities (ISQ), B is the symbol of the ''bel (acoustics), bel'', a unit of logarithmic power ratio named after 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 (dB), for signal strength and sound pressure level 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 Music is the art of arranging sounds in time to produce a composition through the elements of melody, harmony, rhythm, and timbre. It is one of the universal cultural Culture () is ...
is defined as the symbol for octet in IEC 80000-13 and is commonly used in languages such as French language, French and Romanian language, Romanian, 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 10; other systems are based on powers of 2. Nomenclature for these systems has been the subject of confusion. Systems based on powers of 10 reliably use standard SI prefixes ('Kilo-, kilo', 'Mega-, mega', 'Giga-, giga', ...) and their corresponding symbols (k, M, G, ...). Systems based on powers of 2, however, might use binary prefixes ('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 rate units, data transfer rates in computer networks, internal bus, hard drive and flash media transfer speeds, and for the capacities of most storage media, particularly hard drives, Flash memory, flash-based storage, and DVDs. It is also consistent with the other uses of the SI prefixes in computing, such as Hertz#Computing, CPU clock speeds or FLOPS, measures of performance.


Units based on powers of 2

A system of units based on powers of 2 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, IEC, 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 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 operating system, and random-access memory capacity, such as main memory and CPU cache size, and in marketing and billing by telecommunication companies, such as Vodafone,
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
, Orange S.A., Orange and Telstra.


History of the conflicting definitions

Contemporary computer memory has a Binary addressing, binary architecture making a definition of memory units based on powers of 2 most practical. The use of the metric prefix ''kilo'' for binary multiples arose as a convenience, because 1024 is approximately 1000. This definition was popular in early decades of personal computing, with products like the Tandon Corporation, Tandon 5-inch double density, DD floppy format (holding 368,640 bytes) being advertised as "360 KB", following the 1024-byte convention. It was not universal, however. The Shugart Associates, Shugart SA-400 5-inch floppy disk held 109,375 bytes unformatted, and was advertised as "110 Kbyte", using the 1000 convention. Likewise, the 8-inch Digital Equipment Corporation, DEC RX01 floppy (1975) held 256,256 bytes formatted, and was advertised as "256k". Other disks were advertised using a ''mixture'' of the two definitions: notably, -inch HD disks advertised as "1.44 MB" in fact have a capacity of 1,440 KiB, the equivalent to 1.47 MB or 1.41 MiB. In 1995, the International Union of Pure and Applied Chemistry's Interdivisional Committee on Nomenclature and Symbols attempted to resolve this ambiguity by proposing a set of binary prefixes for the powers of 1024. In December 1998, the International Electrotechnical Commission, IEC addressed such multiple usages and definitions by creating prefixes such as kibi, mebi, gibi, etc., to unambiguously denote powers of 1024. Thus the kibibyte (KiB), represents 210  bytes = 1024 bytes. These prefixes are now part of the IEC 80000-13, International System of Quantities. The IEC further specified that the kilobyte should only be used to refer to 1000 bytes. The IEC adopted the proposal and published the standard in January 1999.Amendment 2 to IEC International Standard IEC 60027-2: Letter symbols to be used in electrical technology - Part 2: Telecommunications and electronics. In 1999, Donald Knuth suggested calling the kibibyte a "large kilobyte" (''KKB'').


Lawsuits over definition

Lawsuits arising from alleged consumer confusion over the binary and decimal definitions as applied to the byte have generally ended in favor of the manufacturers, with courts holding that the legal definition of gigabyte or GB is 1 GB = 1,000,000,000 (109) bytes (the decimal definition) rather than the binary definition (230). Specifically, the courts held that "the U.S. Congress has deemed the decimal definition of gigabyte to be the 'preferred' one for the purposes of 'U.S. trade and commerce' [...] The California Legislature has likewise adopted the decimal system for all 'transactions in this state.'" Earlier lawsuits had ended in settlement with no court ruling on the question, such as a lawsuit against drive manufacturer Western Digital. Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity. Seagate was sued on similar grounds and also settled.


Practical examples


Common uses

Many programming languages define the data type ''byte''. The C (programming language), C and C++ programming languages define ''byte'' as an "''addressable unit of data storage large enough to hold any member of the basic character set of the execution environment''" (clause 3.6 of the C standard). The C standard requires that the integral data type ''signedness, unsigned char'' must hold at least 256 different values, and is represented by at least eight bits (clause 5.2.4.2.1). Various implementations of C and C++ reserve 8, 9, 16, 32, or 36 bits for the storage of a byte. In addition, the C and C++ standards require that there are no gaps between two bytes. This means every bit in memory is part of a byte. Java (programming language), Java's primitive byte data type is always defined as consisting of 8 bits and being a signed data type, holding values from −128 to 127. .NET programming languages, such as C#, define both an unsigned byte and a signed sbyte, holding values from 0 to 255, and two's complement, −128 to 127, respectively. In data transmission systems, the byte is defined as a contiguous sequence of bits in a serial data stream representing the smallest distinguished unit of data. A transmission unit might include start bits, stop bits, or parity bits, and thus could vary from 7 to 12 bits to contain a single 7-bit ASCII code.


See also

* Data * Data hierarchy * JBOB, Just a Bunch Of Bytes * Nibble * Octet (computing) * Primitive data type * Tryte * Qubyte (quantum byte) * Word (computer architecture)


Notes


References


Further reading

* * Ashley Taylor. “Bits and Bytes.” Stanford. https://web.stanford.edu/class/cs101/bits-bytes.html {{Data types Data types Units of information Binary arithmetic Computer memory Data unit Primitive types 1950s neologisms 8 (number)