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Odd Parity Error Detection

A man holding a magnifying glass close to his eye.  Source: Microsoft.

In the odd parity system the parity bit is used to ensure that the total number of 1's when added together equals an odd number. Odd parity works by counting the number of 1's and if the total is odd then the parity bit is set to zero and if it is even the parity bit is set to one. Thus, the total number of 1's in the byte is always odd.

No Error Detected Error Detected
11000001 11000011
01000011 01000010


Parity error detection is not perfect because it can only detect a single bit error in a character, ie: a single zero changed to one or vice versa, but not a double bit error. If there are two errors they will effectively cancel each other out while the correct parity is maintained. In fact, a parity check will detect any error, which corrupts an odd number of bits, but will fail to detect one which corrupts an even number of bits.

Click here to review the wikipedia resource on parity.

Next: Error Detection: Block Check Sum