ABSTRACT
A parity bit in a binary code word is a bit added to ensure that the number of bits with the value 1 in the code word is even or odd. Parity bits are used as the simplest form of error detecting codes. If the code consists of code words with an even (odd) number of 1’s, it is called an even (odd) parity check code. In the case of an even (odd) parity check code, given k bits of information, an extra bit is added so that the total number of 1’s in a code word is even (odd). For example, in an even parity check code with 4 information bits, the addition of the parity check bit at the beginning consists of the following 16 code words:
Parity check codes were used on magnetic data storage, punched tape data in data communication and processing systems in the early 1950s. For example, on the systems sold by the British company ICL in the 1950s, the 1-inch-wide paper tape had eight hole positions running across it, with the eighth being reserved for a parity bit.
