How a computer finds one flipped bit and fixes it: Hamming's code

A bit can flip in memory, on a disk or in a radio signal, and nothing tells you which one went wrong. In 1950 Richard Hamming published a code that finds the bad bit and flips it back.

Three overlapping parity checks cover seven bits. When one bit flips, exactly the checks that cover it fail, and the pattern of failures spells out that bit's position in binary. Break one yourself and watch it heal.