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parity bit
Because old modems transmitted data one character at a time, each character had to have its own individual error check. The usual rule was to add an extra bit (the parity bit) at the end of each character before the stop bit. This bit would be set to 0 or 1 based on the value of the previous data bits. These days, modems gather data into packets and send a larger 2- or 4-byte error-check value to validate data in the entire packet. So a parity bit is no longer necessary. |