A parity bit is a binary digit (bit) that is added to data to make the number of 1’s either even (in even parity) or odd (in odd parity). It’s a simple error detection scheme to check the integrity of data.
How It Works:
- If the number of 1’s in a given set of data is odd, the parity bit is set to 1.
- If the number of 1’s is even, the parity bit is set to 0.
- This ensures that the total number of 1’s, including the parity bit, is always even.
- If the number of 1’s in a given set of data is even, the parity bit is set to 1.
- If the number of 1’s is odd, the parity bit is set to 0.
- This ensures that the total number of 1’s, including the parity bit, is always odd.
- When data is transmitted or stored, a parity bit is added based on the original data.
- When the data is read or received, the parity is checked. If it doesn’t match the expected even or odd parity, an error is detected.
Let’s consider a byte of data: 11010101.
- For even parity, since there are 5 ones in the data, the parity bit would be set to 1 to make the number of ones even (total 6 ones). The transmitted byte would be: 110101011.
- For odd parity, the parity bit would be set to 0 (because there are already an odd number of ones). The transmitted byte would be: 110101010.
- Simple to Implement: Requires minimal hardware or software overhead.
- Quick Detection: Can quickly detect single-bit errors.
- Limited Error Detection: Can only detect an odd number of bit errors. It cannot detect errors when an even number of bits have changed (since the parity would still appear correct).
- No Error Correction: While it can detect some errors, it doesn’t indicate where the error is or provide a means to correct it.
In practical applications, parity is often used in combination with other error detection and correction techniques, especially where higher reliability is required.