US Patent 7225208 Systems and methods for backing up data files

A system for backing up data files generates information from which those files can be recovered, and it sends that information to a back-up location. To determine what information to send, it generates summaries of those files from time to time and identifies changed locations by comparing the summaries with one another. As a consequence, the information it sends the back-up location can be limited to the identities and new contents of the locations thereby identified.