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. The size of the byte has historically been hardware dependent and no definitive standards existed that mandated the size. The de facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte. 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 optimize for this common usage. The popularity of major commercial computing architectures has aided in the ubiquitous acceptance of the 8-bit size.
The unit octet was defined to explicitly denote a sequence of 8 bits because of the ambiguity associated at the time with the byte. The usage of the term octad(e) for 8 bits is no longer common today
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The unit symbol for the byte is specified in IEC 80000-13, IEEE 1541 and the Metric Interchange Format as the upper-case character B.
In other contexts, B is the symbol of the bel, a unit of logarithmic power ratios named after Alexander Graham Bell. The usage of B for byte therefore conflicts with this definition. It is also not consistent with the SI convention that only units named after persons should be capitalized. However, there is little danger of confusion 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, i.e. the decibyte, is never used.
The unit symbol kB is commonly used for kilobyte, but may be confused with the still often-used abbreviation of kb for kilobit. IEEE 1541 specifies the lower case character b as the symbol for bit; however, IEC 80000-13 and Metric-Interchange-Format specify the abbreviation bit (e.g., Mbit for megabit) for the symbol, providing disambiguation from B for byte.
The lowercase letter o for octet is defined as the symbol for octet in IEC 80000-13 and is commonly used in several non-English languages (e.g., French and Romanian), and is also used with metric prefixes (for example, ko and Mo)