Question

I have faced that in my computer architecture course at university.
I can’t understand the parity bit; Why it has two kinds of even and odd.

Can anyone give me clear explain about parity codes?

Answer 1

A ‘parity bit’ is a method of error checking. Imagine that you need to send 8 bits over a connection and determine whether they got through right. You could try sending it twice, that way if there is an error, the receiver will know because the two messages differ. However, this requires two times the bandwidth, which is too much. So often every byte (8 bits) will also have a parity bit. You count up the number of ones in the byte. If it is odd, the parity bit is one. If it is even, the parity bit is zero. That way if there is any single error the receiver will know and only one eighth the extra bandwidth is needed. Examples:

Data: 01001001  3 ones, parity bit 1
Data: 00110101  4 ones, parity bit 0

If receiver gets 00111101 and parity bit 0, it will know that there is some corruption.

Of course if there are two errors in the same byte there will be no way to detect this – example if original is 00000001 and received is 00000010 – but this is considered to be rare enough to not worry for most applications.