The RZ structure, being based on the Unix file system with the addition of cycles or versions as in the VMS operating system, provides an excellent base for the FATMEN file catalogue. In an RZ database, a directory contains data identified by a number of keys. In the FATMEN file catalogue, these keys include the filename (i.e. that part of the generic name that follows the last slash, the pathname maps directly to the RZ pathname), the location code, medium type and copy level (original, copy, copy of a copy etc.). Further information, currently some 600 bytes per file, is stored in ZEBRA banks; one per file. Full details of the contents of the RZ and ORACLE databases are to be found in the users guide section of this manual. To summarize, they contain all information that is required to access transparently the data, plus ample space for user information, such as comments, bit encoded information, integer data etc. More information on ZEBRA and the RZ package are to be found in the ZEBRA users' guide.