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Bit

Bit is the amount of information contained in a yes-or-and answer to a question having two equally probable answers. Simultaneously it measures a a computational quantity which can be stored in one of two values such as 0 or 1, or TRUE or FALSE.

The Information Technology Vocabulary (Part 1: Fundamental Terms) INCITS/ISO/IEC 2382-1-1993 (formerly ANSI/ISO/IEC 2382-1-1993) defines in article 01.02.08. Bit; Binary digit as Either of the Digits  0 or 1 when used in the Binary system.

In connection with an information content we can speak about fraction of a bit, for instance a storage cell with three storage possibilities has information content of typeset structure, but physically no storage cell can contain bit fractions. More generally, the information content of an information source with typeset structure equally probable outputs is typeset structure.  In information theory also other units for measuring of the amount information are used:   hartley is a unit of information equal to one of ten possible, i.e. typeset structure, or natural unit (nat) which uses natural logarithm (to the base e) instead of the logarithm to the base 2 . Here a information source with typeset structure equally probable outputs has typeset structurenats.

In graphics the bits are used to describe each dot. A 1-bit image is monochrome; an 8-bit image supports 256 colors or grayscales; and a 24- or 32-bit graphic supports true color.

Computers are often classified by the number of bits they can process at one time or by the number of bits they use to represent addresses. These two values are theoretically (and practically) not always the same. For instance, a computer classified as a 32-bit machine might have its data registers (or address identifiers) 32 bits wide.

A caution is recommended in using the prefixes kilo-, mega-, giga-, etc., and their symbols k/K, M, G, etc. in the binary sense.

An SI prefix 1  (the so called metric prefix) is associated to a symbol that precedes to form a decimal multiple or submultiple of a unit of measure. In binary prefixes (IEC 60027-2/IEEE 1541) used in computing  each successive prefix is multiplied by 1024 rather than the 1000 used by the SI prefix system.  The reason for this is the usage of powers contrary to powers of ten used in everyday life. In January 1999, the International Electrotechnical Commission introduced the prefixes kibi-, mebi-, gibi-, etc., and the corresponding symbols Ki, Mi, Gi, etc. to specify binary multiples of a quantity and to distinguish them from the metric usage.  

 Name                                                                                          ... sp;  152    921    504    606    846    976

Thus according to the standard SI definition  1 kilobit = 1 000 bit, but in the alternate binary definition 1 kilobite=1 Kib („kibibit”)=1 024bit, etc.

Bit is an equivoque with English “bit” and as such it was coined  by American statistician John Wilder Tukey while working with John von Neumann on early computer design.  The history of the word is dimmish. One story says that Tukey invented the term bit as a contraction of  Binary digIT during a seminar held in winter 1943/44 in Princeton on the initiative of mathematician Norbert Wiener. According to other sources (Annals of the History of Computing) Tukey invented this world over a lunch table in 1946. The term bit subsequently  replaced the words binit or bigit used in the same sense till early 1970s (for instance, it is reported that E.Teller used bigit every time). 2

In a print form the word bit appears for the first time in C.E.Shannon’s famous paper The Mathematical Theory of Communication in Bell Systems Technical Journal in 1948 with a reference to Tukey.

Notes

1 From the French Système International d’Unités  that is International System of Units.

2 Note that Tukey was the first person to use the word software to describe the programs on which electronic calculators ran in a 1958 article in the American Mathematical Monthly.  He also named the Fast Fourier Transform, and contributed to and named the fields of linear programming and exploratory data analysis.

Cite this web-page as:

Štefan Porubský: Bit.

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