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== Storage access methods ==
Storage-oriented access methods in approximate chronological order:
* [[BDAM]] - [[Basic direct access method]]
* [[Basic sequential access method|BSAM]] <!-- the acronym links to other topic --> - [[Basic sequential access method]]
* [[QSAM]] - [[Queued sequential access method]]
* [[BPAM]] - [[Basic partitioned access method]]
* [[ISAM]] - [[Indexed sequential access method]]
* [[VSAM]] - [[Virtual storage access method]], introduced with [[OS/VS]]
* [[Object access method|OAM]] <!-- the acronym links to other topic -->  - [[Object access method]], introduced in MVS/SP (1989)
* [[Distributed Data Management Architecture]] - access methods for distributed file access.

=== Basic versus queued ===
Both types of access deal with [[storage record|records]] of a [[data set (IBM mainframe)|data set]]. ''Basic'' access methods read or write one physical record &ndash; block &ndash; at a time.  ''Queued'' methods support internal [[Block (data storage)|blocking]] of data and also often read-ahead scheme.<ref name=aus/> Queued access methods generally provide better performance, while basic methods provide more flexibility.

=== Sequential versus direct ===
''Sequential'' access assumes that records can be processed only sequentially, as opposed to ''direct'' (or random) access. Some devices, such as [[magnetic tape data storage|magnetic tape]], naturally enforce sequential access, but it can be used as well on [[direct access storage device]]s (DASD), such as disk drives. In the latter case, a data set written with sequential access can be later processed in a direct manner.