parity

In communications, a simple form of error checking that uses an extra or redundant bit after the data bits but before the stop bit or bits. Parity may be set as follows:

• Odd Indicates that the sum of all the 1 bits in the byte plus the parity bit must be odd. If the total is already odd, the parity bit is set to zero; if it is even, the parity bit is set to one.
• Even If the sum of all the 1 bits is even, the parity bit must be set to zero; if it is odd, the parity bit must be set to one.
• Mark The parity bit is always set to one and is used as the eighth bit.
• Space The parity bit is set to zero and is used as the eighth bit.
• None If parity is set to none, there is no parity bit, and no parity checking is performed.

The parity settings used by both communicating computers must match. Most online services, such as CompuServe or America Online, use no parity and an 8-bit data word.

See also asynchronous transmission; parity checking; parity error.