Memory chips with built-in error-checking typically use a method known as parity to check for errors.
Parity chips have an extra bit for every 8 bits of data. The way parity works is simple. Let's look at even parity first.
When the 8 bits in a byte receive data, the chip adds up the total number of 1s. If the total number of 1s is odd, the parity bit is set to 1. If the total is even, the parity bit is set to 0.
When the data is read back out of the bits, the total is added up again and compared to the parity bit. If the total is odd and the parity bit is 1, then the data is assumed to be valid and is sent to the CPU. But if the total is odd and the parity bit is 0, the chip knows that there is an error somewhere in the 8 bits and dumps the data.
Odd parity works the same way, but the parity bit is set to 1 when the total number of 1s in the byte are even.