Parity generation and checking are a critical aspect of ensuring that a digital data transfer occurs without errors in the bit sequences.  A parity generator scans through a stream of digital bits and adds what is called a parity bit.  A parity bit represents a certain sequence of data, more in the next paragraph.  When the signal reaches the destination, that parity bit is checked against the data stream and if there are any inconsistencies.  This is known as error detection.

 

A generator counts a sequence of bits and determines how many of those bits are 1.  There are two forms of parity bits, odd and even.  If an even parity bit is being used, the generator adds a bit to the sequence that ensures the entire length of bits has an even number of 1s.  If an odd parity bit is used, a value is added to the end of the sequence that ensures the entire grouping has an even count.  For example, if an even parity generator looks at sequences of 7 bits and sees that there are three 1s and four 0s, it adds a new bit to the end that is 1.  This makes the group have four 1s and have an even count.

The checker scans the data at a receiving end and determines if the parity bit and the data bits align, or the even or odd count is correct.  If they do not, it means there was a transmission error and the data has to be discarded or sent again.