A-level Computing/AQA/Paper 2/Fundamentals of data representation/Error checking





Parity Checking
Parity checking is only able to detect an odd number of errors and cannot correct the errors detected.

Even Parity
The number of 1s is counted, and if the number of 1s is even then the parity bit is set to 0, else it is set to 1.

Odd Parity
The number of 1s is counted, and if the number of 1s is odd then the parity bit is set to 0, else it is set to 1.

Majority Vote
Interference can occur which can cause 1's to be received as 0's and vice versa. Therefore, a system called majority voting is used.

'Majority voting is where each bit is represented by three bits to try and curb damage from interference.'

-Found from AQA Computer Science AS Level Textbook

Check Digits
Check digits are digits added to identification numbers (e.g. bank numbers and product codes (e.g. UPC)) where the number will sometimes be entered manually. They are similar to parity bits but are intended to detect human entry error.