A method and system of the present invention generates a representation of a new version of an original file system with reference to the original file system and the new version of the file system. Use of data from previous versions of the file system reduces the amount of data to be stored in the delta directory map file, delta modification data block file, and delta look up table generated for the data portions unique to the newest version of an original file system. The inventive process produces delta data block records that identify the location of data portions that may be used to generate the newest version of the file system. The data portions may be located in a file in the original file system, a delta modification data block file in a previous version of the original file system or a delta modification data block file for the newest version of the original file system. The method of the present invention is performed by generating a basis index table identifying the data content of an original file system, generating a file of modification data blocks that may be used to modify the data content of the original file system, and generating a delta look up table that identifies the location of the data blocks used to represent the newest version of the original file system. The delta look up table and the file of modification data blocks may be stored for delivery to a computer on which a copy of the original file system is stored. The delta look up table and the file of modification data blocks are then used by the computer system on which a copy of the original file system is stored to provide the data content for a new version of the original file system. This is done in way that appears to provide a single file system containing the new version of the file system. Thus, the method of the present invention may be used to generate data for updating the content of a copy of the original file system without having to generate a copy of every file and data block for the new content of the original file system.