Parity bits are used as the simplest form of error detecting code.
Parity bits are generally applied to the smallest units of a communication protocol, typically 8-bit octets bytesalthough they can also be applied separately to an entire message string of bits. The parity bit ensures that the total number of 1-bits in the string is even or odd.
In the case of even parity, for a given set of bits, the occurrences of bits whose value is 1 are counted. If that count is odd, the parity bit value is set to 1, making the total count of occurrences of 1s in the whole set including the parity bit an even number.
If the count of 1s in a given set of bits is already even, the parity bit's value is 0. In the case of odd parity, the coding is reversed.
For a given set erori pe binar bits, if the count of bits with a value of 1 is even, the parity bit value is set to 1 making the total count of 1s in the whole set including the parity bit an odd number. If the count of bits with a value of 1 is odd, the count is already odd so the parity bit's value is 0.
If a bit is present at a point otherwise dedicated to a parity bit but is not used for parity, it may be referred to as a mark parity bit if the parity bit is always 1, or a space parity bit if the bit is always 0. In such cases where the value of the bit is constant, it may be called a stick parity bit even though its function has nothing to do with parity.