 Parity checks can
detect
all
odd number
of
bit errors
 Each error will
change the
number of
1 bits:
 by +1:
Before: 11100111 (6 1's)
After: 11101111 (7 1's)

or
 −1
Before: 11100111 (6 1's)
After: 11100011 (5 1's)


 An odd number of
bit errors will result in:

Example:
Original data (unprotected): 1111000
Even parity: 11110000
Data with 1 bit error: 11010000
===> 1 bit error results in odd parity !!!
(error detected !!)

 Parity checks can
not detect an
even
number
of bit errors
Example:
Original data (unprotected): 1111000
Even parity: 11110000
Data with 2 bit errors: 11010100
===> 2 bit errors results in even parity !!!
Error cannot be detected !!!

