Error Detection

Error Detection

Memory hardware supports two general types of error detection: parity and ECC.

• Parity: Parity methods append either a 1 or 0 to each byte so that the total number of 1s is always either even or odd. Parity methods can detect errors in only one bit. Parity methods can detect errors, but cannot fix them because they cannot determine the specific bit with the error. The parity error checking method is older and has almost been completely eclipsed by the new ECC method.
• Error Correcting Code (ECC): ECC methods append a value to the end of each byte so that the value of the data can be compared and recalculated if an error occurs. Error Correcting Code is an improvement on parity techniques because errors in more than one bit can be detected and corrected.

For a computer to implement parity or ECC, the memory and system board hardware must be built to support these techniques. This is because the hardware must store and transfer parity or ECC information as well as other data and instructions. Servers and high-end workstations usually use memory with built-in memory checking.