What Is Parity Checking?

Parity checking has its limitations.

Parity checking is a simple method of detecting errors between data being written to computer memory and read back again. It requires an older type of computer memory, known as parity memory and, in newer computers, a BIOS ("Basic Input Output System") setting to be enabled.

Data

Each character that is stored in computer memory is represented by one byte, or 8 bits, of data. Each bit has a value of zero or one, so in each byte there will be an odd or even number of ones.

How it Works

Parity checking examines each byte of data and sets a ninth bit--known as a parity bit--to one if the number of ones is odd and zero if the number of ones is even. This means that a correct byte will always have an odd number of ones and if it does not, when the data is read back from memory, an error is reported.

Limitations

Parity checking can detect an error in one bit of data in a byte, but not two. Similarly, it cannot detect which of the bits in a byte of data is invalid and so cannot perform error correction.

References

• The PC Guide: Parity Checking
• Technick.net: Error Checking