Abstract: Techniques for converting file-systems used for organizing and storing data on computer readable mediums are disclosed. A first file-system is converted to a second file-system while file(s) stored on the computer readable medium remain(s) virtually undisturbed in the same location. A FAT file-system (e.g., FAT32) is converted to an HFS file-system (e.g., HFS Plus) by generating HFS data structures (Catalog, Allocation File and Extents) for file(s) already stored in the HFS file-system. The number and location of the file(s) can be determined primarily based on the FAT file-system's data structures (FAT and Directory). The conversion process can be stopped before the FAT file-system indicators (partition map and boot sector) are overwritten.