Definition and Characteristics of a Byte
– A byte is a unit of digital information.
– It consists of eight bits.
– It is the smallest addressable unit of memory in many computer architectures.
– Network protocol documents refer to an 8-bit byte as an octet.
– The size of the byte historically varied, but the de facto standard is eight bits.
– Early encoding systems used six-bit and nine-bit bytes.
– Memory words in early systems corresponded to 2, 3, 4, 5, 6, 8, or 10 six-bit bytes.
– The modern standard of eight bits allows values from 0 to 255.
– The 8-bit byte is widely accepted in major commercial computing architectures.
– Modern architectures typically use 32- or 64-bit words.
Etymology and History of the Byte
– The term ‘byte’ was coined in 1956 during the design phase for the IBM Stretch computer.
– Another origin of ‘byte’ is attributed to Louis G. Dooley in the context of an air defense system called SAGE.
– Early computers used four-bit and six-bit codes for representation.
– ASCII, a seven-bit coding system, replaced teleprinter codes in the 1960s.
– IBM introduced the eight-bit EBCDIC encoding scheme in the 1960s.
Unit Symbol and Multiple-Byte Units
– The unit symbol for the byte is an uppercase ‘B.’
– The term ‘octet’ is used to unambiguously specify a size of eight bits.
– The lowercase letter ‘o’ is used as the symbol for octet in some languages and combined with metric prefixes.
– The unit symbol ‘B’ conflicts with the symbol for the bel, a unit of logarithmic power ratio.
– The bel is rarely used, while the byte is widely used.
– Multiple-byte units based on the byte include kilobyte, megabyte, gigabyte, etc.
– Different interpretations of these units create confusion.
– The decimal interpretation is about 2% smaller than the binary interpretation for the kilobyte.
– Ambiguity arises when using the prefixes M or G.
– The use of binary prefixes (Ki, Mi, Gi) or the symbols (K, M, G) can help clarify the interpretation.
Units based on powers of 10 and Units based on powers of 2
– Kilobyte (kB) is defined as 1,000 bytes by the International Electrotechnical Commission (IEC).
– The IEC standard defines eight multiples up to 1 yottabyte (YB), equal to 1000 bytes.
– Additional prefixes, ronna- for 1000 and quetta- for 1000, were adopted by the International Bureau of Weights and Measures (BIPM) in 2022.
– This definition is commonly used for data-rate units in computer networks, internal bus, hard drive and flash media transfer speeds, and storage media capacities.
– Operating systems like macOS, iOS, Ubuntu, and Debian use this definition.
– Kibibyte (KiB) is defined as 1,024 bytes by the international standard IEC80000-13.
– The IEC standard defines eight multiples up to 1 yobibyte (YiB), equal to 1024 bytes.
– The binary counterparts to ronna- and quetta- were proposed as robi- (Ri, 1024) and quebi- (Qi, 1024) but have not been adopted.
– An alternative system called the customary convention uses KB for 1,024 bytes, MB for 1024 bytes, and GB for 1024 bytes.
– The customary convention is used by Microsoft Windows, telecommunications companies, and memory capacity measurements.
Parochial Units and History of the Conflicting Definitions
– Various computer vendors have coined terms for data of different sizes.
– Examples include double word, half word, long word, quad word, slab, superword, syllable, and informal terms like half byte and nybble.
– Some vendors use terms like octal K for 1000.
– These terms can have different sizes even within a single vendor.
– Parochial units are not standardized and can cause confusion.
– Early personal computing used a binary architecture, making powers of 2 practical for memory units.
– The use of the metric prefix kilo for binary multiples arose as a convenience.
– Different products and disks advertised capacities using either the 1,024-byte convention or the 1,000 convention.
– The International Union of Pure and Applied Chemistry (IUPAC) proposed binary prefixes in 1995.
– In 1998, the IEC adopted the proposed prefixes to unambiguously denote powers of 1024.
– The IEC adopted the IUPAC proposal and published the standard in January 1999.
– The IEC prefixes are part of the International System of Quantities.
– The kilobyte should only be used to refer to 1,000 bytes according to the IEC.
– The adoption of standard definitions aims to resolve ambiguity and confusion.
– The IEC prefixes are widely used in the field of computing and data storage.
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 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. Those bits in an octet are usually counted with numbering from 0 to 7 or 7 to 0 depending on the bit endianness.
| byte | |
|---|---|
| Unit system | unit derived from bit |
| Unit of | digital information, data size |
| Symbol | B, o (when 8 bits) |
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. 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. In this era, bit groupings in the instruction stream were often referred to as syllables 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. 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. 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). Internationally, the unit octet, symbol o, explicitly defines a sequence of eight bits, eliminating the potential ambiguity of the term "byte".
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