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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.〔(【引用サイトリンク】title=Computer History Museum - Exhibits - Internet History - 1964 )〕 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. ==History== The term ''byte'' was coined by Werner Buchholz in July 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'' to avoid accidental mutation to ''bit''.〔 Early computers used a variety of four-bit binary coded decimal (BCD) representations and the six-bit codes for printable graphic patterns common in the U.S. Army (Fieldata) and Navy. 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, 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 characters 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 eight-bit Extended Binary Coded Decimal Interchange Code (EBCDIC), an expansion of their six-bit binary-coded decimal (BCDIC) representation 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 introduced digital telephony first on long-distance trunk lines. 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 microprocessors in the 1970s popularized this storage size. Microprocessors such as the Intel 8008, the direct predecessor of the 8080 and the 8086, used in early personal computers, could also perform a small number of operations on the four-bit 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'' is used to unambiguously specify a size of eight bits. It is used extensively in protocol definitions. Historically, the term ''octad'' or ''octade'' was used to denote 8 bits as well at least in Western Europe;〔〔 however, this usage is no longer common today. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Byte」の詳細全文を読む スポンサード リンク
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