Virtual Storage Access Method: Difference between revisions

Revision as of 22:29, 6 August 2005

Revision as of 22:32, 6 August 2005

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'''Virtual Storage Access Method''' ('''VSAM''') is an [[IBM]] disk file storage scheme first used in the [[S/370]] operating system and later used throughout the [[MVS]] architecture. VSAM comprises four access methods: [[KeyedKey SequentialSequenced 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 thence into larger divisions called Control Areas (CAs). Control Interval sizes are measured in bytes — e.g. 4K — while Control Area sizes are measured in disk tracks or cylinders.