parity checking

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Related to parity checking: Odd parity, Even parity

parity checking

An error detection technique that tests the integrity of digital data in the computer. Parity checking adds an extra parity cell to each 8-bit byte of memory, thus creating a nine-bit structure.

In an "even parity" system, a 0 is stored in the parity bit if there is an even number of bits in the byte; if an odd number, a 1 is stored to make the total number of bits even. In "odd parity" systems, the opposite occurs; a 0 parity bit if odd, a 1 parity bit if even to make the total number odd.

Only Good for One-Bit Errors
Each time a byte is transferred, the parity bit is checked. One-bit parity systems will detect if one of the eight bits in the byte has been erroneously switched from 1 to 0 or from 0 to 1. However, it cannot detect a two-bit error, because if two bits in the byte are reversed, the even or odd number remains the same. Error-correcting code (ECC) is a more robust memory checking system (see ECC memory).

Plenty of "NO" Parity Around
There are 12% more memory cells in 9-bit parity chips than there are in 8-bit memory. To shave costs, many computers are built with non-parity memory, and it is truly a miracle that the billions of non-parity computers work as well as they do. See RAID, ECC memory and soft error.
References in periodicals archive ?
The newly updated S2A9550 is the only storage array on the market that detects and corrects 'silent data corruption' inherent in SATA drives by performing on-the-fly real-time parity checking on all read I/Os without incurring any performance penalty.
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With hardware RAID 6 and parity checking of all read I/Os, the S2A9550 allows large capacity applications to implement a reliable online or nearline active archive that can scale up to 720 TB in a two rack solution -- up to 5 times more dense and scaleable than other comparable disk based storage systems.