There are two conditions which can cause a parity checking mechanism to fail to detect errors properly.

  • Parity Bit Corruption - Corruption of the parity bit itself during transmission can cause the receiving station to discard valid data.
  • Data Bit Corruption - Corruption of more than one bit in the byte/word will leave the number of binary 1's in the byte the same, but change the data's actual value. This corrupts the data but prevents the receiving device from detecting the error because parity still matches
  • Combination - Both the parity bit and a bit in the data is corrupted such that the data and parity bit match, but the data is corrupted.

All of these conditions occur frequently enough to make parity checking somewhat unreliable. Parity checks are often disabled and more effective methods are used to verify the integrity of the data such as cyclic redundancy checks.

 

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