Virtual Storage Access Method: Difference between revisions

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'''Virtual Storage Access Method''' ('''VSAM''') is an [[IBM]] disk file storage scheme first used in the [[OS/360|OS/VS2]] operating system and later used throughout the [[MVSMultiple Virtual Storage]] (MVS) architecture. The [[record-oriented filesystem]] of VSAM comprises four access methods: [[Key Sequenced Data Set]] (KSDS), [[Relative Record Data Set]] (RRDS), [[Entry Sequenced Data Set]] (ESDS) and [[Linear Data Set]] (LDS). See [[record-oriented filesystem]].

VSAM records can be of fixed or variable length. They are organised in fixed-size blocks called Control Intervals (CIs), and then into larger divisions called Control Areas (CAs). Control Interval sizes are measured in bytes — e.g.for 4Kexample 4 [[kilobyte]]s — while Control Area sizes are measured in disk tracks or cylinders.

The utility program IDCAMS is commonly used to manipulate ("delete and define") VSAM [[Dataset|datasets]]. Custom programs can access VSAM datasets through data definitions (DD'sDDs) in Job Control Language ([[Job Control Language|JCL]]) or in online regions such as [[CICS]]in (Customer Information Control Systems. ([[CICS]]).

Both [[IMS/DB]] and [[IBM DB2|DB2]] are implemented on top of VSAM and use its underlying [[Data_structure|data structures]].

==See also==

* [[Job Control Language|JCL]] (JCL)

* [[IBM mainframe utility programs]]

* [[ISAM]]

* [[Geneva ERS]]

==References==

* http://www.redbooks.ibm.com/redbooks/SG246105/wwhelp/wwhimpl/js/html/wwhelp.htm

==External links==

==See also==

* [[CICS]]

* [[Job Control Language|JCL]]

* [[IBM_mainframe_utility_programs]]

* [[ISAM]]

* [[Geneva ERS]]

* [http://www.tiburontech.com/vsam.htm VSAM Support - IBM Software ]

[[Category:IBM Mainframe computer operating systems]]