Parity/Non-parity Check

Early transmission codes had a serious problem in that a bit could be lost or gained in transmission because of an electrical or mechanical failure/ If the loss went undetected, the character received on the other end of the lime was incorrect. To Prevent this from happening, a parity check system was developed. Each character is represented by a byte consisting of a combination of intelligence bits (seven bits in ASCII and eight bits in EBCDIC) and an additional bit called a check or parity bit. Even parity codes place a check bit with each byte that contains an uneven number of 1 bits. (Remember that a bit is either 1 or o). Because the check bit is transmitted only with characters composed of an uneven number of 1 bits,all characters transmitted will have n even number of 1 bits. The check bit is transmitted to and from the computer along with character code. If a bit is lost (or added) in transmission, the system will detect its loss. An uneven number of 1 bits received in a code string composed of even bits will signal an error. Odd Parity codes add a check bit to code combinations that have an even number of 1 bits. Thus,all characters transmitted have an odd number of bits. Odd and even parity care similar in nature. They are both designed to signal an error in the even that data are lost or added.