OS-Queued and Basic Access Method

Operating systems generally provide many access methods. These are sometimes grouped into two categories, namely queued access methods and basic access methods. The queued methods provide more powerful capabilities than the basic methods.

Queued access methods are used when the sequence in which records are to be processed can be anticipated, such as in sequential and indexed sequential accessing. The queued methods perform anticipatory buffering and scheduling of I/O operations. They try to have the next record available for processing as soon as the previous record has been processed.

The basic access methods are normally used when the sequence in which records are to be processed cannot be anticipated such as in direct accessing. And also in user applications to control record access without incurring the overhead of the queue method.
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