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Even parity refers to a parity checking mode in asynchronous communication systems in which an extra bit, called a parity bit, is set to zero if there is an even number of one bits in a one-byte data item. If the number of one bits adds up to an odd number, the parity bit is set to one.
Even parity checking may also be used in testing memory storage devices.
Parity bits are added to transmitted messages to ensure that the number of bits with a value of one in a set of bits add up to even or odd numbers. Even and odd parities are the two variants of parity checking modes.
Even parity can be more clearly explained by means of an example. Consider the transmitted message 1010001, which has three ones in it. This is turned into even parity by adding a one, making the sequence 1 1010001, so that there are four ones (an even number). If the transmitted message has the form 1101001, which is already an even number, a zero is added to sustain the even parity. The resulting message is 0 1101001, so that an even number of ones remains in the transmitted message.
Even parity checking is also used in testing memory storage devices. However, in order for this to work, the sender and receiver should agree to use even parity checking as the basic error detection technique. If a single bit is switched during transmission, parity checks can detect that the data is corrupted. However, even parity may fail to detect errors introduced when an even number of bits in the same data unit is altered due to electrical noises.