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The checksum is used as an indicator of data integrity: The receiving system also computes a checksum and then compares its value with the one received. If they are different, there is an error in the data--or possibly in the checksum. Although the Internet itself doesn't guarantee any provisions for automatic transmission in such cases, many individual Internet programs include an automatic retransmission feature at the packet or file level. In the early days of computing, checksums were often simply arithmetical sums of the bits that ignored carry bits too large for the checksum space. Now, most systems use more sophisticated algorithms such as cyclic rendundancy checks (CRCs) or even error-detection and correction codes (EDACS).
