Host system data files are written directly to a large erase block flash memory system with a unique identification of each file and offsets of data within the file but without the use of any intermediate logical addresses or a virtual address space for the memory. Directory information of where the files are stored in the memory is maintained within the memory system by its controller, rather than by the host. Each data file is uniquely identified in a file directory, which points to entries in a file index table (FIT) of data groups that make up the file and their physical storage locations in the memory.