Vannevar Bush had written in 1936 of "bits of information" that could be stored on the punched cards used in the mechanical computers of that time. Tukey, who had written a Bell Labs memo on 9 January 1947 in which he contracted "binary information digit" to simply "bit". Shannon first used the word "bit" in his seminal 1948 paper " A Mathematical Theory of Communication". Ralph Hartley suggested the use of a logarithmic measure of information in 1928. The encoding of text by bits was also used in Morse code (1844) and early digital communications machines such as teletypes and stock ticker machines (1870). In all those systems, the medium (card or tape) conceptually carried an array of hole positions each position could be either punched through or not, thus carrying one bit of information. A variant of that idea was the perforated paper tape. The encoding of data by discrete bits was used in the punched cards invented by Basile Bouchon and Jean-Baptiste Falcon (1732), developed by Joseph Marie Jacquard (1804), and later adopted by Semyon Korsakov, Charles Babbage, Hermann Hollerith, and early computer manufacturers like IBM. Use of the latter may create confusion with the capital "B" which is the international standard symbol for the byte. The symbol for the binary digit is either "bit" as per the IEC 80000-13:2008 standard, or the lowercase character "b", as per the IEEE 1541-2002 standard. As a unit of information, the bit is also known as a shannon, named after Claude E. In information theory, one bit is the information entropy of a random binary variable that is 0 or 1 with equal probability, or the information that is gained when the value of such a variable becomes known. Frequently, half, full, double and quadruple words consist of a number of bytes which is a low power of two. It may be physically implemented with a two-state device.Ī contiguous group of binary digits is commonly called a bit string, a bit vector, or a single-dimensional (or multi-dimensional) bit array.Ī group of eight bits is called one byte, but historically the size of the byte is not strictly defined. The relation between these values and the physical states of the underlying storage or device is a matter of convention, and different assignments may be used even within the same device or program.
These values are most commonly represented as either " 1" or " 0", but other representations such as true/ false, yes/ no, on/ off, or +/ − are also widely used. The bit represents a logical state with one of two possible values. The name is a portmanteau of binary digit. The bit is the most basic unit of information in computing and digital communications.
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