Source : Free On-Line Dictionary of Computing

Virtual Storage Access Method
     
         (VSAM) An {IBM} disk file storage scheme first used
        in {S/370} and virtual storage.  VSAM comprises three access
        methods: {Keyed Sequenced Data Set} (KSDS), {Relative Record
        Data Set} (RRDS), and {Entry Sequenced Data Set} (ESDS).
     
        Both {IMS/DB} and {DB2} are implemented on top of VSAM and use
        its underlying data structures.
     
        ["Storage" or "Sequential"?]
     
        (2002-07-26)