Paritetsbits

Paritetsbits, or parity bit, is a simple error-detecting mechanism used in digital communication and storage. It is a single binary digit added to a data word to help determine whether an error has occurred during transmission or retrieval.

There are two common schemes: even parity and odd parity. In even parity, the parity bit is chosen so that the total number of 1s in the data plus the parity bit is even. In odd parity, the total is odd. The parity bit is computed from the data and transmitted or stored alongside it. Upon receipt, the parity is checked; if it does not match, a single-bit error is detected.

Applications for parity bits include some asynchronous serial communications, where a parity configuration may be specified in the frame format (for example, some UART settings use even or odd parity). Parity bits have also been used in older memory systems that employ parity memory to detect single-bit errors during access. In these contexts, the parity bit provides a low-cost, low-latency means of detecting errors without complex processing.

Limitations exist: a parity bit can only reliably detect an odd number of bit errors within the word; it cannot detect all error patterns, such as even numbers of bit flips, and it cannot indicate which bit is wrong or correct the data. For higher reliability, more powerful error-detecting or correcting codes are used, such as two-dimensional parity, Hamming codes, or cyclic redundancy checks.

See also: ECC memory, Hamming code, CRC, error detection and correction.