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ビット

出典: フリー百科事典『ウィキペディア（Wikipedia）』 (2023/04/10 13:38 UTC 版)

ビット (bit) は、情報理論、コンピューティング、多くのデジタル通信における情報の基本単位（英語版）である。ビットは、コンピューティングでの二値ストレージやデジタル通信における二値シンボルのことも意味し、そのストレージ・シンボルには、（情報量の単位としての）1ビットの情報を記憶・符号化できる。二進数の1桁のことであり、その名前はbinary digitの2語の一部を組み合わせた語（かばん語）である^[1]。

脚注

^ Coded Character Sets, History and Development (1 ed.). Addison-Wesley Publishing Company, Inc.. (1980). p. x. ISBN 978-0-201-14460-4. LCCN 77--90165. オリジナルの2016-11-18時点におけるアーカイブ。 2016年5月22日閲覧。 [1]
^ Understanding Information Transmission, (2006)
^ Digital Communications, (2006)
^ IEEE Std 260.1-2004
^ “Units: B”. 2016年5月4日時点のオリジナルよりアーカイブ。2019年10月1日閲覧。
^ Information theory and coding. McGraw-Hill. (1963)
^ ^a ^b “A Mathematical Theory of Communication”. Bell System Technical Journal 27 (3): 379–423. (July 1948). doi:10.1002/j.1538-7305.1948.tb01338.x. hdl:11858/00-001M-0000-002C-4314-2. オリジナルの1998-07-15時点におけるアーカイブ。. "The choice of a logarithmic base corresponds to the choice of a unit for measuring information. If the base 2 is used the resulting units may be called binary digits, or more briefly bits, a word suggested by J. W. Tukey."
^ “A Mathematical Theory of Communication”. Bell System Technical Journal 27 (4): 623–666. (October 1948). doi:10.1002/j.1538-7305.1948.tb00917.x. hdl:11858/00-001M-0000-002C-4314-2.
^ A Mathematical Theory of Communication. University of Illinois Press. (1949). ISBN 0-252-72548-4. オリジナルの1998-07-15時点におけるアーカイブ。
^ “Instrumental analysis”. Bulletin of the American Mathematical Society 42 (10): 649–669. (1936). doi:10.1090/S0002-9904-1936-06390-1. オリジナルの2014-10-06時点におけるアーカイブ。.
^ National Institute of Standards and Technology (2008), Guide for the Use of the International System of Units. Online version. Archived 3 June 2016 at the Wayback Machine.
^ “Why is a byte 8 bits? Or is it?”. Computer History Vignettes (2000年8月8日). 2017年4月3日時点のオリジナルよりアーカイブ。2017年4月3日閲覧。 “[…] With IBM's STRETCH computer as background, handling 64-character words divisible into groups of 8 (I designed the character set for it, under the guidance of Dr. Werner Buchholz, the man who DID coin the term "byte" for an 8-bit grouping). […] The IBM 360 used 8-bit characters, although not ASCII directly. Thus Buchholz's "byte" caught on everywhere. I myself did not like the name for many reasons. […]”
^ “7. The Shift Matrix”. The Link System. IBM. (1956-06-11). pp. 5–6. Stretch Memo No. 39G. オリジナルの2017-04-04時点におけるアーカイブ。 2016年4月4日閲覧. "[…] Most important, from the point of view of editing, will be the ability to handle any characters or digits, from 1 to 6 bits long […] the Shift Matrix to be used to convert a 60-bit word, coming from Memory in parallel, into characters, or "bytes" as we have called them, to be sent to the Adder serially. The 60 bits are dumped into magnetic cores on six different levels. Thus, if a 1 comes out of position 9, it appears in all six cores underneath. […] The Adder may accept all or only some of the bits. […] Assume that it is desired to operate on 4 bit decimal digits, starting at the right. The 0-diagonal is pulsed first, sending out the six bits 0 to 5, of which the Adder accepts only the first four (0-3). Bits 4 and 5 are ignored. Next, the 4 diagonal is pulsed. This sends out bits 4 to 9, of which the last two are again ignored, and so on. […] It is just as easy to use all six bits in alphanumeric work, or to handle bytes of only one bit for logical analysis, or to offset the bytes by any number of bits. […]"
^ “The Word "Byte" Comes of Age...”. Byte Magazine 2 (2): 144. (February 1977). "[…] The first reference found in the files was contained in an internal memo written in June 1956 during the early days of developing Stretch. A byte was described as consisting of any number of parallel bits from one to six. Thus a byte was assumed to have a length appropriate for the occasion. Its first use was in the context of the input-output equipment of the 1950s, which handled six bits at a time. The possibility of going to 8 bit bytes was considered in August 1956 and incorporated in the design of Stretch shortly thereafter. The first published reference to the term occurred in 1959 in a paper "Processing Data in Bits and Pieces" by G A Blaauw（英語版）, F P Brooks Jr and W Buchholz（英語版） in the IRE Transactions on Electronic Computers, June 1959, page 121. The notions of that paper were elaborated in Chapter 4 of Planning a Computer System (Project Stretch), edited by W Buchholz, McGraw-Hill Book Company (1962). The rationale for coining the term was explained there on page 40 as follows:
Byte denotes a group of bits used to encode a character, or the number of bits transmitted in parallel to and from input-output units. A term other than character is used here because a given character may be represented in different applications by more than one code, and different codes may use different numbers of bits (ie, different byte sizes). In input-output transmission the grouping of bits may be completely arbitrary and have no relation to actual characters. (The term is coined from bite, but respelled to avoid accidental mutation to bit.)
System/360 took over many of the Stretch concepts, including the basic byte and word sizes, which are powers of 2. For economy, however, the byte size was fixed at the 8 bit maximum, and addressing at the bit level was replaced by byte addressing. […]"
^ Buchholz-1962Buchholz, Werner, ed. (1962), “Chapter 4: Natural Data Units” (PDF), Planning a Computer System – Project Stretch, McGraw-Hill Book Company, Inc. / The Maple Press Company, York, PA., pp. 39–40, LCCN 61--10466, オリジナルの2017-04-03時点におけるアーカイブ。 2017年4月3日閲覧。
^ “A proposal for a generalized card code of 256 characters”. Communications of the ACM 2 (9): 19–23. (1959). doi:10.1145/368424.368435.
^ ^a ^b Information in small bits Information in Small Bits is a book produced as part of a non-profit outreach project of the IEEE Information Theory Society. The book introduces Claude Shannon and basic concepts of Information Theory to children 8+ using relatable cartoon stories and problem-solving activities.