Talk:Access method
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What's different?
editThis 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
editUnlike 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)
- Well, after writing in Talk:Execute Channel Program I thought I would mention this here, but it seems that I already did. The comparison to device drivers on other systems isn't quite right, as those normally run in system space and supervisor mode. It is an unusual feature of OS/360, as it allows keeping the OS kernel and transient space smaller. Since Unix also started on systems with small memory, it isn't so obvious how the differences came out the way they did. Gah4 (talk) 19:55, 26 May 2020 (UTC)
External links modified
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NPOV
editAccess methods, but not the name, were around[1][2][3][4][5][6][7] prior to OS/360. Further, There is no Start I/O instruction on current IBM mainframes, and the low level details of I/O are different[a] on different mainframes. The text needs to be split into generic and IBM specific, and the IBM specific section needs to take into account the change in I/O architecture from System/360 and System/370 to System/370 Extended Architecture (S/370-XA) through zArchitecture.
If there are any editors with, e.g., Burroughs, GE, RCA, experience, please help broaden the article. Shmuel (Seymour J.) Metz Username:Chatul (talk) 00:17, 17 July 2020 (UTC)
- Can we end at EXCP, which is where access methods end, and not mention SIO? (Presuming that they still do EXCP when needed.) Gah4 (talk) 00:00, 18 July 2020 (UTC)
- Also, there doesn't seem to be a page for SIO. Should there be one? Gah4 (talk) 00:00, 18 July 2020 (UTC)
- What did DEC RMS call these things? Peter Flass (talk) 16:00, 17 July 2020 (UTC)
- DEC used the terms file, record, File Access Block (FAB) and Record Access Block (RAB); was that what you are asking?
- I've never used Record Management Services[8] explicitly, although I did briefly use VAX/VMS for text editing and document formatting. I was surprised to see that there was no RMS (VMS) article, and certainly consider it noteworthy. Shmuel (Seymour J.) Metz Username:Chatul (talk) 20:23, 17 July 2020 (UTC)
Notes
- ^ E.g., some mainframes don't have channel programs; each I/O operation handles only a single block. In fact, the low level details may differ between two channels on the same processor, e.g., 7604 and 7907 on the IBM 7070.
References
- ^ GE-635 File and Record Control Reference Manual. GE. CPB-1003.
- ^ Reference Manual Input/Output Control System for the IBM 705 III. IBM. C28-6109.
- ^ Reference Manual, IBM 709/7090 Input/output Control System (PDF). IBM. C28-6100-2.
- ^ IBM 7070/7074 Input/Output Control System for IBM 729 Magnetic Tape Units, Unit Record Equipment (7070-IO-904). IBM. C28-6175-3.
- ^ IBM 7070/7074 Input/Output Control System for IBM 1301 and 1302 Disk Storage (7070-IO-940). IBM. C28-6272-1.
- ^ Reference Manual IBM 7080 Input/Output Control System for use with 729 Magnetic Tape Units (PDF). IBM. 1962. C28-6237-0.
- ^ RCA 3301 Realcom Training Manual (PDF). RCA EDP Division. November 1964. 94-06-000.
- ^ VAX-11 Record Management Services Reference Manual (PDF). DEC. February 1979. AA-D031B-TE.
It seems that there is Record_Management_Services found through RMS. Gah4 (talk) 00:04, 18 July 2020 (UTC)
- I've added a redirect. Shmuel (Seymour J.) Metz Username:Chatul (talk) 01:51, 19 July 2020 (UTC)