Editing Bit (section)

{{short description|Unit of information}}
{{About|the unit of information}}
{{Use dmy dates|date=December 2020|cs1-dates=y}}
{{Fundamental info units}}

The '''bit''' is the most basic [[Units of information|unit of information]] in [[computing]] and digital [[communication]]. The name is a [[portmanteau]] of '''binary digit'''.<ref name="Mackenzie_1980"/> The bit represents a [[truth value|logical state]] with one of two possible [[value (computer science)|values]]. These values are most commonly represented as either {{nowrap|"{{mono|1}}" or "{{mono|0}}"}}, but other representations such as ''true''/''false'', ''yes''/''no'', ''on''/''off'', or ''+''/''−'' are also widely used.

The relation between these values and the physical states of the underlying [[Data storage device|storage]] or [[computing device|device]] is a matter of convention, and different assignments may be used even within the same device or [[computer program|program]]. It may be physically implemented with a two-state device.

A contiguous group of binary digits is commonly called a ''[[bit string]]'', a bit vector, or a single-dimensional (or multi-dimensional) ''[[bit array]]''. A group of eight bits is called one&nbsp;''[[byte]]'', but historically the size of the byte is not strictly defined.<ref name="Bemer_2000"/> Frequently, half, full, double and quadruple words consist of a number of bytes which is a low power of two. A string of four bits is usually a ''[[nibble]]''.

In [[information theory]], one bit is the [[information entropy]] of a random [[Binary number|binary]] variable that is 0 or 1 with equal probability,<ref name="Anderson_2006"/> or the information that is gained when the value of such a variable becomes known.<ref name="Haykin_2006"/><ref name="IEEE_260"/> As a [[unit of information]], the bit is also known as a ''[[shannon (unit)|shannon]]'',<ref name="Rowlett"/> named after [[Claude E. Shannon]].  As a measure of the length of a digital string that is encoded as symbols over a 0-1 (binary) alphabet, the bit has been called a binit,<ref>{{cite book |last1=Breipohl |first1=Arthur M. |title=Adaptive Communication Systems |date=1963-08-18 |publisher=University of New Mexico |page=7 |url=https://digitalrepository.unm.edu/ece_etds/425/ |access-date=7 January 2025}}</ref> but this usage is now rare.<ref>{{cite dictionary |title=binit |url=https://www.thefreedictionary.com/binit |dictionary=The Free Dictionary |access-date=7 January 2025}}</ref>

In [[data compression]], the goal is to find a shorter representation for a string, so that it requires fewer bits when stored or transmitted; the string would be compressed into the shorter representation before doing so, and then decompressed into its original form when read from storage or received. The field of [[algorithmic information theory]] is devoted to the study of the irreducible information content of a string (i.e., its shortest-possible representation length, in bits), under the assumption that the receiver has minimal ''a priori'' knowledge of the method used to compress the string. In [[error detection and correction]], the goal is to add redundant data to a string, to enable the detection or correction of errors during storage or transmission; the redundant data would be computed before doing so, and stored or transmitted, and then checked or corrected when the data is read or received.

The symbol for the binary digit is either "bit", per the [[IEC 80000-13]]:2008 standard, or the lowercase character "b", per the [[IEEE 1541-2002]] standard. Use of the latter may create confusion with the capital "B" which is the international standard symbol for the byte.