A method of providing information for error detection, usually calculated by summing a set of values.
The checksum is usually appended to the end of the data that it is calculated from so that they can be compared. For example, Xmodem, a popular file-transfer protocol, uses a 1-byte checksum calculated by adding all the ASCII values for all 128 data bytes and ignoring any numeric overflow. The checksum is added to the end of the Xmodem data packet. This type of checksum does not always detect all errors. In later versions of the Xmodem protocol, cyclical redundancy check (CRC) is used instead for more rigorous error control.
See also cyclical redundancy check; error detection and correction.