Importance

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Abstract

A system backs up computer files to a remote site via modem, LAN, WAN, or other network device 16. Files of a user computer that are found in a common library at the remote site initially are not copied to the remote site, whereas files not in the library are copied to the remote site and potentially automatically added to the library when a sufficient number of computers contain the files. Then, periodically or continuously if the user is online via the modem, the user computer determines which blocks have been changed, and the user computer transmits only changed blocks to the remote site. The blocks are gathered in 'chunk' files, and when a chunk file reaches a predetermined size, it is transmitted to the remote site for updating the back up version of the respective file. The process then resumes identifying changed blocks. In addition to flagging the changed block for transfer, the process resynchronizes the local data file with the backed up version using a two-step comparison, first comparing the first two characters in the block with a pre-stored character set, and then, if the first comparison results in a match, comparing a digital signature of the changed block with a pre-stored signature. If either comparison results in a mismatch, the test is repeated using, as the first byte of the test block, the next byte in the sequence. Novel encryption procedures are also disclosed.

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First Claim