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Ease of programming - programmer would no longer deal with a specific device procedures, including error detection and recovery tactics in each and every program. A program designed to process a sequence of 80-character records would work no matter where the data are
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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
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that enables access to data on disk, tape or other external devices. Access methods were present in several mainframe operating systems since the late 1950s, under a variety of names; the name
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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.
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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.
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of data and also often read-ahead scheme. Queued access methods generally provide better performance, while basic methods provide more flexibility.
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363:, and different ways of accessing data, such as via record keys. Access methods provide programs a way of dealing with this complexity.
518:(DASD), such as disk drives. In the latter case, a data set written with sequential access can be later processed in a direct manner.
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access methods) or allow the operation to be started and the program to continue to run, waiting for the completion at a later time (
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Programs can read or write a record or block of data and wait until the input/output operation is complete (
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M. A. Auslander, D. C. Larkin, A. L. Scherr: "The
Evolution of the MVS Operating System", pages 478-479
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This is a different use of the term from the other access methods mentioned in this article.
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in non-mainframe operating systems, but typically provide a greater level of functionality.
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Programs can specify the type of error recovery to be used in case of input/output errors.
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System/360 and successor systems perform input/output using a special program for an
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access methods read or write one physical record – block – at a time.
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Read-ahead - Queued access methods may start as many I/O operations as there are
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instruction issued by the operating system. This is usually front ended by the
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access assumes that records can be processed only sequentially, as opposed to
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for programmers to transfer data to or from device, and could be compared to
355:, where all files and devices are considered to be an unformatted stream of
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514:, naturally enforce sequential access, but it can be used as well on
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Network-oriented access methods in approximate chronological order:
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Storage-oriented access methods in approximate chronological order:
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available, anticipating application program requirements.
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operating system, two elements provide access methods:
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108:. Unsourced material may be challenged and removed.
577:- Transmission Control Protocol/Internet Protocol
318:) macro for application programmer convenience.
16:APIs in IBM mainframe computer operating systems
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651:Partitioned Hierarchical Direct Access Method
625:Hierarchical Indexed Sequential Access Method
466:- access methods for distributed file access.
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681:Simple Hierarchical Sequential Access Method
278:operating system. Access methods provide an
71:Learn how and when to remove these messages
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510:(or random) access. Some devices, such as
209:. Please do not remove this message until
615:Hierarchical Indexed Direct Access Method
247:Learn how and when to remove this message
229:Learn how and when to remove this message
168:Learn how and when to remove this message
766:ABCs of z/OS System Programming Volume 3
562:Virtual telecommunications access method
464:Distributed Data Management Architecture
205:Relevant discussion may be found on the
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280:application programming interface (API)
962:Computer-related introductions in 1963
535:Basic telecommunications access method
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635:Hierarchical Sequential Access Method
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595:Generalized Sequential Access Method
106:adding citations to reliable sources
544:Queued teleprocessing access method
274:was introduced in 1963 in the IBM
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645:Overflow sequential access method
605:Hierarchical Direct Access Method
588:IBM Information Management System
52:This article has multiple issues.
553:Telecommunications access method
436:Indexed sequential access method
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967:IBM mainframe operating systems
475:Both types of access deal with
427:Basic partitioned access method
418:Queued sequential access method
93:needs additional citations for
60:or discuss these issues on the
409:Basic sequential access method
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516:direct access storage devices
460:, introduced in MVS/SP (1989)
445:Virtual storage access method
351:Unlike systems derived from
671:Partitioned Secondary Index
324:supervisor call instruction
211:conditions to do so are met
29:Input/Output Control System
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752:November 19, 2008, at the
400:Basic direct access method
33:Record Management Services
21:Record-oriented filesystem
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522:Networking access methods
491:methods support internal
290:Purpose of access methods
25:Record (computer science)
778:"Types of IMS databases"
499:Sequential versus direct
329:Access methods provide:
312:Execute Channel Program
705:Modern implementations
387:Storage access methods
957:Computer file systems
826:OS/360 and successors
720:Communications Server
717:Data Facility Product
304:channel command words
458:Object access method
102:improve this article
471:Basic versus queued
263:is a function of a
198:of this article is
564:, introduced with
447:, introduced with
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781:. Retrieved
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100:Please help
95:verification
92:
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54:Please help
51:
296:I/O channel
158:August 2012
951:Categories
725:References
504:Sequential
196:neutrality
128:newspapers
57:improve it
19:See also:
837:Low-level
265:mainframe
219:July 2020
207:talk page
63:talk page
750:Archived
493:blocking
481:data set
308:START IO
200:disputed
914:Network
863:Storage
854:STARTIO
709:In the
675:PSIMDEX
647:(OSAM),
477:records
379:memory.
361:records
345:buffers
334:stored.
142:scholar
849:EXCPVR
695:SHISAM
687:), and
665:PHIDAM
571:TCP/IP
508:direct
489:Queued
369:queued
276:OS/360
144:
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31:, and
685:SHSAM
655:PHDAM
629:HISAM
619:HIDAM
566:OS/VS
485:Basic
479:of a
449:OS/VS
373:basic
357:bytes
149:JSTOR
135:books
936:VTAM
931:TCAM
926:QTAM
921:BTAM
900:VSAM
895:ISAM
890:BPAM
885:QSAM
880:BSAM
875:BDAM
870:XDAP
844:EXCP
828:I/O
785:2011
711:z/OS
639:HSAM
609:HDAM
599:GSAM
586:The
573:for
558:VTAM
549:TCAM
540:QTAM
531:BTAM
441:VSAM
432:ISAM
423:BPAM
414:QSAM
405:BSAM
396:BDAM
353:Unix
320:EXCP
316:EXCP
193:The
121:news
905:OAM
582:IMS
575:MVS
454:OAM
259:An
104:by
953::
733:^
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560:-
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