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Parity is a mathematical term that defines a value as even or odd. For example, the number 4 has an even parity, while the number 5 has an odd parity. When even and odd values are compared, such as 4 and 5, they are considered to have different parity. If two even or odd values are compared with each other, they have the same parity.
In computer science, parity is often used for error checking purposes. For example, a parity bit may be added to a block of data to ensure the data has either an even or odd parity. This type of error detection is used by various data transmission protocols to ensure that data is not corrupted during the transfer process. If the protocol is set to an odd parity, all packets received must have an odd parity. If it is set to even, all packets must have an even parity. Otherwise, a data transmission error will occur and the corresponding packet(s) will need to be resent.
Parity is also used in a type of computer memory called parity RAM. This type of RAM stores a parity bit with each byte of data to validate the integrity of each byte. Therefore, 9 bits of data are required for every byte stored in the RAM. While parity RAM was commonly used in early computers, memory has become more reliable and therefore most systems now use non-parity RAM. High-end workstations and servers, which require consistent data integrity, typically use ECC RAM, which provides a more advanced means of error checking than standard parity RAM.