A bit (a contraction of 'binary
digit') is the basic unit of information in computing and telecommunications. In computing, a bit can be defined as a variable or computed quantity that can have only two possible values. These two values are often interpreted as binary digits and are usually denoted by the numerical digits 0 and 1. The two values can also be interpreted as logical values (true/false)
, algebraic signs (+/-), activation states (on/off), or any other two-valued attribute. The correspondence between these values and the physical states of the underlying storage or device is a matter of convention.
A bit can be implemented in hardware by means of a two state device and can be stored by a digital device or other physical system that exists in either of two possible distinct states. Any number can be represented by any sequence of bits, which in turn may be represented by any mechanism capable of being in two mutually exclusive states such as relays
, vacuum tubes
or mechanical means (e.g. plates and rods)
. The numeric value represented in each case is dependent upon the value assigned to each symbol. These may be the two stable states of a flip-flop, two positions of an electrical switch, two distinct voltage or current levels allowed by a circuit, two directions of magnetization or polarization, etc. In most modern computing devices, a bit is usually represented by an electrical voltage or current pulse, or by the electrical state of a flip-flop circuit.
A punched tape
is a mechanical
way to store bits.
All computers built by Konrad Zuse
notation for numbers.