input/output operation is complete (queued access methods) or allow the operation to be started and the program to continue to run, waiting for the completion at a later time (basic access methods). Programs can specify the size and number of buffers for a file. The same buffer or pool can be used for multiple files, allowing blocks of data to be read from one file and written to another without requiring data movement in memory. Programs can specify the type of error recovery to be used in case of input/output errors. Storage access methods Storage-oriented access methods in approximate chronological order: BDAM - Basic direct access method BSAM - 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 OAM - 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 records of a data set. Basic access methods read or write one physical record – block – at a time. Queued methods support internal blocking of data and also often read-ahead scheme. 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, naturally enforce sequential access, but it can be used as well on direct access storage devices (DASD), such as disk drives. In the latter case, a data set written with sequential access can be later processed in a direct manner. Networking access methods Network-oriented access methods in approximate chronological order: BTAM - Basic telecommunications access method QTAM - Queued teleprocessing access method TCAM - Telecommunications access method VTAM - Virtual telecommunications access method, introduced with OS/VS TCP/IP for MVS - Transmission Control Protocol/Internet Protocol IMS The IBM Information Management System (IMS) uses the term "access method" to refer to its methods for manipulating "segments in a database record". These are: Generalized Sequential Access Method (GSAM), Hierarchical Direct Access Method (HDAM), Hierarchical Indexed Direct Access Method (HIDAM), Hierarchical Indexed Sequential Access Method (HISAM), Hierarchical Sequential Access Method (HSAM), Overflow sequential access method (OSAM), Partitioned Hierarchical Direct Access Method (PHDAM), Partitioned Hierarchical Indexed Direct Access Method (PHIDAM), Partitioned Secondary Index (PSIMDEX), Simple