paritetsbiter

Paritetsbiter, commonly called parity bits in English, are small pieces of data added to a block of binary data to help detect errors that occur during storage or transmission. They are used in simple error-detection schemes where the parity bit is chosen so that the total number of 1s in the block, including the parity bit, is even (even parity) or odd (odd parity).

In typical usage, a parity bit accompanies every data unit, often a byte. When the receiver obtains the data, it recomputes the parity and compares it with the transmitted parity. If the parity check fails, at least one bit has likely flipped during transmission, and an error is detected. Parity bits can detect any odd number of bit errors across the data and parity bit, but fail for even numbers of errors, including two-bit errors, and they do not indicate which bit is wrong.

Limitations and applications: Parity bits provide only basic error detection and cannot correct errors. For stronger protection, more advanced codes such as Hamming codes or ECC (error-correcting code) memory are used. Parity memory was common in older computer systems and remains present in some configurations, though many modern systems rely on ECC RAM for both detection and correction, while parity RAM is less common.

In telecommunications, parity bits have historically been used in serial links and other simple protocols as a lightweight error-detection mechanism. Today, they are often supplemented or replaced by more robust techniques such as CRCs and forward error correction.