The FATMEN system is based upon a layer model, comprising the following components.
The file catalogue is provided by the FATMEN package. Layers above the file catalogue are typically experiment specific, or at least vary from experiment to experiment. Thus, the CERN collaboration ALEPH and the DESY group H1 both use BOS as a data structure management package, whereas many other collaborations use ZEBRA. Similarly, the L3 collaboration has developed the DBL3 package as a production database, whereas OPAL uses a system named OPCAL.
The layers below the FATMEN file catalogue are typically system, or at least site dependant. For example, CERN uses different staging systems on the central IBM and Siemens systems, the central VAX cluster and the Cray. In addition, staging software also exists on the L3 Apollos and the SHIFT facility. All of these systems are interfaced to FATMEN in a manner that is completely transparent to the user.
The Media Management System, which at CERN is the Tape Management System (TMS) developed at the Rutherford Appleton Laboratories in the UK, may again be substituted by another package, or be missing altogether. User exits are provided for the case when FATMEN is installed at a site without a media management system, and an interface already exists to the Systems Center VMTAPE product.