Content deleted Content added
Peter Flass (talk | contribs) →Purpose of access methods: read-ahead |
Peter Flass (talk | contribs) →Purpose of access methods: buffer |
||
Line 9:
* Ease of hardware replacement - programmer would no longer alter a program when data should be migrated to newer model of storage device, provided it supports the same access methods.<ref name=aus/>
* Ease shared data set access - an access method is a trusted program, that allows multiple programs to access the same file, while ensuring the basic data integrity and system security.<ref name=aus/>
* Read-ahead - Queued access methods may start as many I/O operations as the are [[data buffer|buffers]] available, anyicipating application program requirements.
Unlike systems derived from [[Unix]], where all files and devices are considered to be an unformatted stream of [[byte]]s, mainframes offer a variety of data options and formats, such as varying types and sizes of [[record (computer science)|records]], and different ways of accessing data, such as via record keys. Access methods provide programs a way of dealing with this complexity.
* Programs can read or write a record or block of data and wait until the 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).
| |||