Talk:MVS

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[edit] Post-MVS features

Should features mentioned on this page be moved to the OS/390 page if they first appeared in OS/390 or to the z/OS page if they first appeared in z/OS? Guy Harris 02:13, 3 February 2006 (UTC)

Presumably this would be covered by the reorganization discussed below. Guy Harris 18:27, 19 October 2007 (UTC)

[edit] 31-bit addressing

MVS originally supported 24-bit addressing. As the underlying hardware progressed it supported 31-bit (XA and ESA) and now (as z/OS) 64-bit addressing.
Should this say "it supported 32-bit (XA and ESA)"? I'm not aware of any odd-bit-length addressing schemes, but I don't consider myself knowledgeable enough to be comfortable changing the article on the basis of an assumption.Southcutt 02:36, 12 April 2006 (UTC)

I'm not an expert, but I have the impression the topmost bit in an address had a special meaning or was otherwise reserved; the 31-bit page discusses this, but not in enough detail. Diving into the appropriate Principles of Operation manual would probably give more detail (and perhaps more detail than you want :-)). Guy Harris 02:49, 12 April 2006 (UTC)
I'm not an expert, but I coded in assembler on these machines for a long time. OK, maybe I'm something of an expert. Anyway, "31-bit" is correct. There was an early attempt at 32-bit addressing in the System/360 Model 67, and the weird bugs deriving from unsigned addresses in a milieu where sign bits hadn't previously participated were legion. When Extended Addressing (XA) can back, it did it in 31-bit form to avoid repeating those problems. When System/390 extended the addressing to 64 bits, a lot of us said "surely you mean 63 bits - no sign, right?". The response from IBM was that they had spent so much time and effort dealing with public relations etc. fallout from the 31-vs.-32 bit decision that there was only one acceptable answer to the 63-vs.-64 bit question. RossPatterson 03:48, 12 April 2006 (UTC)
Interesting. How did 64-bit systems handle variable-length argument lists in subroutine calls (see below re CALL macro)?Philcha 05:37, 19 October 2007 (UTC)

The high order bit running in XA mode (31-bit addressing) was typically used to indicate the last element in a series of link listed addresses, i.e. there were not any more tokens in the chain.

That's right. More specifically, from DOS/360 and OS/360 onwards subroutine calls passed the addresses of their arguments (like references in C); the last of a variable-length set of arguments had the high bit set to 1 (by the CALL macro in Assembler; by compilers for high-level languages), and the hardware ignored that bit when using the address to access memory.Philcha 05:37, 19 October 2007 (UTC)

I believe that 31-bit addressing did not become available until MVS/XA. Until then I believe that MVS used 24-bit addressing. I'll have to dig out an old POO to verify. Additionally, I dont' see any reference to MFT an ancestor of MVT.--Les 14:25, 12 December 2006 (UTC)

[edit] Benefit of running MVS now z/OS

MVS will run the processor at 100% utilization while still performing real work. Try that on UNIX or Windows based systems.

More precisely, MVS requires hardly any tuning to run the processor at 100% utilization while still performing real work. In the early 1970s the large UK clearing banks ran their overnight systems at 100% just to get all the work done, but that required careful system design and heavy tuning of MVT. Philcha 06:19, 19 October 2007 (UTC)

[edit] Need to restructure IBM operating system articles?

Long discussion on the topic, with a plan of new structure, has been moved to Talk:History of IBM mainframe operating systems. Please continue there.

--Kubanczyk 12:46, 24 October 2007 (UTC)

[edit] Rewrite of Job Control Language in progress

As part of the proposed restructure of articles on IBM mainframe operating systems (above), I've rewritten Job Control Language to: cover IBM's DOS/360 and its descendants as well as OS/360 and its descendants; focus more on the facilities and flavour of the 2 JCLs rather than on details of some statement types and some of their options. Please comment in Talk: Job Control Language. I'd be particulary grateful for more info on DOS/360 and its descendants, especially after 1980 - I only used DOS JCL a handful of times, and only in the late 1970s.

The rewrite does not currently take account of Truthanado's point in Talk: Job Control Language about use of "JCL" by computer suppliers other than IBM, which may entail further restructuring of articles about JCLs.Philcha 23:47, 20 October 2007 (UTC)

[edit] Name standardization

Some time ago there was a push to standardize the names of articles related to exclusive IBM products (OS/2 → IBM OS/2). I've moved a few of the more obvious ones... would the move here be appropriate? /Blaxthos 17:04, 28 October 2007 (UTC)

How this ummmm "standardization" effort relates to official Wikipedia guideline WP:COMMONNAME? The two seems to be in conflict, aren't they? May I ask about the reasons for this renaming push? --Kubanczyk 17:38, 28 October 2007 (UTC)
Please do not rename until merger proposal decided (see below). If the pages are merged, renaming will be unnecessary. Philcha (talk) 21:10, 25 November 2007 (UTC)

[edit] Merger proposal

To reduce duplication of content re features inherited from MVS's predecessors and to fit into the framework provided by History of IBM mainframe operating systems. —Preceding unsigned comment added by Philcha (talk • contribs) 21:07, 25 November 2007 (UTC)

[edit] Modern definition of MVS?

I'm a person who sometimes uses z/OS but I did not cut my teeth on IBM mainframes. I encounter the term MVS often, so I came here hoping to see a definition, but I don't see what I'm looking for. I'm not looking for "Multiple Virtual Storage" which may be the term's origin but clearly has little relevance to it's current meaning. And I'm not looking for "MVS was the most commonly used operating system on the System/370 and System/390 IBM mainframe computers," (note the past tense), or "MVS is no longer supported by IBM." This may be one meaning of the term, but it is not the way the term is currently used (in my experience). IBM still uses the term widely, see http://www.ibm.com/systems/z/os/zos/bkserv/r9pdf/#mvs, and IBM's usage doesn't fit the definitions presented in this article. If MVS is just an old name for z/OS, then why does IBM still use the term so often, in current publications?

I'm afraid this sounds like a rant. I don't mean it to be, I'm just suggesting that this article should start with the information that most non-mainframe people are going to be looking for -- a straightforward definition of the current meaning of the term. Historical information can come after that. I would suggest a definition to you, if only I knew what it would be. MVS currently seems to be used as a generic term for the non-POSIX portion of z/OS, as far as I can tell, but as a non-expert on the subject I'm not really sure (which is why I turned to Wikipedia). I have not been able to find the answer on the IBM website either. Doctorpepper (talk) 19:27, 19 April 2008 (UTC)

Interesting question. I just googled for "MVS" and found (among a load of irrelevant stuff, nothing to do with IBM OSs):
  • FolDoc on OS/390 - appears to suggest that OS-390 = MVS + Unix. If true, that would support your "MVS currently seems to be used as a generic term for the non-POSIX portion of z/OS".
  • a UK contracts site that is try into recruit for "MVS" contracts - so the term is still in use and widely recognised, despite the fact thatIBM introduced the OS/390 "brand" in 1995.
I'll ask around. Philcha (talk) 20:11, 19 April 2008 (UTC)
I'm afraid that in this field history is important, so if readers don't want to read about the history, they may have serious problems with figuring out anything. In the same way, to provide an example from the PC field, most people say "DOS commands" instead of "Windows Command Prompt commands" (whatever...). Just try to explain this to somebody that does not want to know a bit of DOS/Windows history. --Kubanczyk (talk) 21:16, 19 April 2008 (UTC)