In even parity , it is always the case that the total number of 1 bits is even - if necessary by setting the parity bit to be 1. In odd parity , it is always the case that the total number of 1 bits is odd. Neither - they are equally good but unfortunately unstandardized conventions. Sometimes we need more than detecting errors. By adding extra parity bits, we can correct single-bit and even larger errors.
Parity also becomes an issue with transmitting data from one computer to another via a modem .
It is important that both computers agree on whether to use even, odd, or no parity so the bits can be received properly. It is a piece of hardware that knows how to do a given set of very simple things, such as Fetch a word from memory Simple arithmetical operations, . Test whether a word is all zeros, and if so jump to another part of the program. This collection of simple things a processor can do is called its instruction set . Different types of computers have different instruction sets.