Abstract: A method of transferring a file is executed by a client computer under control of a first program portion and is alsoexecuted by a server computer under control of a second program portion. The server computer stores a baseline file having baseline data. The client computer stores a local file that is a modified baseline file having modified data. The client computer is coupled to the server computer. First tier baseline reference keys are generated for and associated with first tier subsets of the baseline data stored in the baseline file. First tier client reference keys are generated for and associated with first tier subsets of the modified data stored in the local file. When the associated reference keys match, one of the first tier subsets of baseline data is transferred to a destination file stored on the server computer.