Virtual Storage Access Method

Virtual Storage Access Method (VSAM)[1] is an IBM direct-access storage device (DASD) file storage access method, first used in the OS/VS1, OS/VS2 Release 1 (SVS) and Release 2 (MVS) operating systems, later used throughout the Multiple Virtual Storage (MVS) architecture and now in z/OS. Originally a record-oriented filesystem,[NB 2] VSAM comprises four[NB 2] data set organizations: key-sequenced (KSDS), relative record (RRDS), entry-sequenced (ESDS) and linear (LDS).[2] The KSDS, RRDS and ESDS organizations contain records, while the LDS organization (added later to VSAM) contains a sequence of pages with no intrinsic record structure, for use as a memory-mapped file.

  1. ^ "New Life for Legacy Systems at LaBarge". Datamation. May 11, 2007.
  2. ^ Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "1.3.2 Record management". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. p. 5.


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