Talk:Access method

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What's different?[edit]

This page seems to make the distinction in terms of mainframe vs. mini or microcomputer. It seems to me one difference between OS/360 (and successor) access methods, and the device drivers of other systems, is that access methods run in user state (not supervisor state) and use user memory space. (As some point the access methods to EXCP, and pass the generated channel program to the OS to verify aknd run. The OS has to verify that it doesn't do anything that it shouldn't do.) Gah4 (talk) 23:34, 10 April 2015 (UTC)

Access methods do a lot that device drivers don't. Device drivers plus, e.g. ISAM software would be one example. Peter Flass (talk) 03:38, 11 April 2015 (UTC)

Mainf[edit]

Unlike systems derived from Unix, where all files and devices are considered to be an unformatted stream of bytes, mainframes offer a variety of data options Well, at least IBM mainframes. And VMS offers similar file structure (RMS) and VAX is usually not considered a mainframe. Gah4 (talk) 22:30, 5 May 2016 (UTC)

As I understand it, one reason for access methods had to do with the restrictions on OS/360 developers. For one, many control blocks are in user space, and so didn't count against developer quotas. Access methods, I believe, are usually in system space but execute in user mode. Again, this might have related to developer quotas, though it also helps reduce the transitions between problem and supervisor state. See: The_Mythical_Man-Month for some discussion. Gah4 (talk) 22:30, 5 May 2016 (UTC)

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