Talk:IBM System/370

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Contents 1 Recent exchange about 10/7 changes 2 9370 as XA? 3 Extended real addressing 4 Added architecture chapter 5 Violations of backward compatibility

[edit] Recent exchange about 10/7 changes

The following notes address a recent set of changes. User:Spinality|Trevor Hanson]] 21:50, 8 October 2006 (UTC)

1. I began what was intended to be a minor, corrective edit to this article, but it wound up going further than expected. (I'm still uncertain about the contents of the table; I corrected it as well as I could in the available time, but there seems to be some variation in how IBM has referred to its product series. I don't think the -XA architecture designation was an official part of the series name, but just a feature; and that may or may not have been true of the /ESA designation as well.)
2. Based on discussion with Ross Paterson, I removed the compu-hardware-stub template. The article isn't very complete, but it is comparable with entries for other computer systems.
3. The following exchange addresses the -XA and ESA/ tags:

Ross: As I recall it, XA-capable machines were still System/370, and it wasn't until ESA that they broke with the S/370 moniker. Which reminds me - I don't believe I ever heard "ESA" called "System/370-ESA". I was attending the Endicott/Poughkeepsie non-disclosure briefings in those days and it was always described "System/390" or just "ESA". And on a related point, "System/370 compatible" was always a term applied to Amdahl/Fujitsu and National Semiconductor/Hitachi clones, never to IBM machines. The 303x, 4331, and 4341 were genuine S/370. The 308x series almost got called "System/380" (but didn't) because they were the start of XA, which was briefly known inside IBM by that name. RossPatterson 20:28, 8 October 2006 (UTC)

Trevor: This is some of the contradictory stuff that made my edits drag on and on. To answer your specific comments:

• One of the papers I cited talks about ESA/370 in those initial machines. (I pretty much followed the table that somebody else had put here though, which broke the product line down this way.) I removed the term 370-ESA because now I can't find it; I thought I saw that in an early R&D paper late last night but...?.
• I too was surprised to see the term S/370 compatible on an official IBM historical site (I too always thought of 'compatible' as referring to Amdahl/Hitachi/etc., though we usually called them 'PCMs'): http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_basinfo.html. I figure if that's the party line then we better use it. I put a citation in for it in the table though, because I agree this is not how I remember normal terminology at the time. And I can't think of what else to call the 3033.
• I now remember hearing about S/380 also. It's funny how many old factoids start to emerge as you rake over the embers.

Any further clarification from other dinosaurs will be helpful. (As you correct, though, do be sure to look at the IBM citations however, which include terminology that is different from what I remember at the time. But of course "no original research" means my memory is irrelevant!) Trevor Hanson 21:50, 8 October 2006 (UTC)

As is my memory :-) Thanks for recording this, Trevor. RossPatterson 23:17, 8 October 2006 (UTC)

[edit] 9370 as XA?

937X are listed as XA systems.. I strongly believe 9370 were S/370 only systems - Any objection to switch S/370 from XA to S/370 compatible systems in the table ? Ivan Scott Warren 20:02, 16 November 2006 (UTC)

For Info : About the XA vs ESA bit - ESA is an extension to XA.. XA is 31 bits + Subchannels, ESA is XA + Access Registers. S/370 XA did exist as a designation. The designation of ESA/370 to ESA/390 was however, only a name change and there are no architectural differences between the 2. I believe the name ESA/390 was introduced when the ES/9000 series of systems was released. Note : I have no hardproof for any of that, so I'm not going to edit the article without prior consent from the original author.Ivan Scott Warren 20:11, 16 November 2006 (UTC)

I've never been very happy with that table. I did my best to correct it (referencing IBM sources such as this one: http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_FS370C.html), and you see the exchange we had about the odd IBM term 'S/370 compatible'. However I can't find any source that describes the 9370 in detail. (IBM archives has a link to the announcement, but it seems to be broken: http://www-306.ibm.com/common/ssi/OIX.wss?DocURL=http://d03xhttpcl001g.boulder.ibm.com/common/ssi/rep_ca/8/897/ENUS186-178/index.html&InfoType=AN&InfoSubType=null&InfoDesc=Announcement%20Letters&paneltext=Announcements&panelurl=OIX.wss%3Fbuttonpressed%3DNAV002PT090&singlehitflag=false&printableversion=yes) As far as I can see the boulder.ibm.com server is AWOL.)

It would be surprising to me if the 9370, released in 1986(?), was not XA; if not, it would have trouble running the then-current OSes. But I can't remember...and so many 9370s were VSE machines anyway. You may be right that it did not, but I'd be a lot happier if we could find some hard facts on the subject. The whole point of Wikipedia, as you know, is to have material based on published sources rather than people's memories, which are sadly fallible. (As are published sources, of course, but then you can pass the buck.) So to answer your question, of course I don't care if you change it any way you like, it's a collaborative document; but I think the 'right' solution would be to track down some hard facts first. I will keep looking too. Trevor Hanson 21:03, 16 November 2006 (UTC)

Actually, I did own a 9370 (a 9370 Model 55) and I can assure you it wasn't a XA system (It ran VM/SP5, VM/SP6, etc.. which CANNOT run on an XA system).. The successor (the 9221) was the ESA evolution - there was even a MES (Miscelaneous Equipment Specification) upgrade that made it possible to go from the 9370 to the 9221 - which involved - among other things - replacing the 9332 FBA drives with CKD enabled DASDs.. I'm going to try to find definite reference for that - and will include it in the article (that's all if you are OK with it !) Ivan Scott Warren 21:27, 16 November 2006 (UTC)

I finally tracked down some announcement text with a valid link (http://www-306.ibm.com/common/ssi/OIX.wss?DocURL=http://d03xhttpcl001g.boulder.ibm.com/common/ssi/rep_ca/8/897/ENUS186-178/index.html&InfoType=AN&InfoSubType=CA&InfoDesc=Announcement+Letters&panelurl=OIX.wss%3Fbuttonpressed%3DNAV002PT090&paneltext=Announcements) and 9370 appears to have only 8Mb and 16Mb configurations, which adds support to your view. Also, you obviously have much more than vague memories, so I defer to your judgment on this. (And again, I don't care if you change the article any way you like, it's a collaborative document.) Trevor Hanson 21:39, 16 November 2006 (UTC)

Another topic: extended real addressing....[subthread moved to new topic below]

There was one difference between ESA/370 and ESA/390: ESCON. Also, the 3090-J and 4381-91/92 were indeed ESA-capable. Yes, calling it 370/XA was indeed a bit misleading, but you can blame that one on IBM, since they committed it. Jay Maynard 22:08, 16 November 2006 (UTC)

Ah.. And the 4361 is missing from the 43XX line ! (for the record, the 9370 can actually be considered an evolution of the 4361 !) Ivan Scott Warren 22:10, 16 November 2006 (UTC)

I never knew very much at all about the 4361, having never used one. It was always too small for the workloads the shops I worked at ran. Same goes for the 4331, although I did run a couple of 4341s in my time. Jay Maynard 22:57, 16 November 2006 (UTC)

The 4361 was a fun beast.. its particular feature was having all those integrated control units (IFA (Intergated File Adapter, read disk/tape control unit), IPA (Integrated Printer Adapter), ICA (Integrated Commo Adapter) and possibly also an IWA (Integrated Workstation Adapter)) - so you could do without any 3803, 3830|3880, 37xx etc.. One of those few models (the other being the 138) on which you could connect a 3203 model 4 (the one without the control unit) - but I don't think you could go beyond 12MB of storage on it and it was (IIRC) slower than a 4341 (which was rated at a whoping 1.2 MIPS). Ivan Scott Warren 23:26, 16 November 2006 (UTC)

[edit] Extended real addressing

[first few paragraphs moved from above, through "***"]

Another topic: extended real addressing. You added the 4381 and 3090 to the 3033 and 3081, which were the first systems to get this capability (in October 1981). I reworded it to show the timeline more clearly; but I'm not sure that these machines even belong on that list. I believe both were initially released as XA machines (see for example http://www.research.ibm.com/journal/sj/251/tucker.pdf). Of course they had different microcode loads that would turn off XA, but in the timeline they seem to me to go in the next category after extended real addressing. Was there something funny about early 4381/3090 releases? Trevor Hanson 21:39, 16 November 2006 (UTC)

Ok.. More clarifications on that : The 308[1|3|4], The 4381 and the 3090 (and also the [P|R]/390 were all Dual Architecture systems (S/370 and XA or ESA) (Out of the blue : 308x : XA, 3090 XA except S (and maybe J) models which were ESA and 4381 XA except ES-4381 and possibly 4381 the late models 91 and 92 which might have been ESA).. All these had a very distinctive characteristic of having 4K Storage key pages in S/370 mode (STKE instruction available).. the 9370 however, didn't have the option to run in XA or ESA mode (despite the misleading ES/9370 brand name) and as a matter of fact (known fact - no written proof (yet)) had a 2K storage key pages system (STKE instruction not available) which is a tell tale sign of non-XA capability ! Now - On the other side - I've also noticed announcements to be down on the IBM site - which doesn't help ! The denomination S370/XA system in the table is what is misleading since S/370, XA and ESA are *architectures* but not *technologies* - however - IBM may have linked the capability to run said architecture to said technology (i.e : Machine X can run S/370 and XA architecture and is therefore considered a XA ..system) Ivan Scott Warren 21:46, 16 November 2006 (UTC)

I found this buried in the 9370 announcement letter (my stress added):

In February IBM announced four new models of the IBM 4381, expanding our System/370 data center offerings and providing significant new levels of price performance. The recently enhanced 4381 family with its multiple channel, high data rates, and large memory capabilities provides an attractive entry solution for System/370 data center environments -- as well as a low-cost entry into System/370 extended addressing architecture. The 4381 offers an excellent growth path for current IBM 4341 and 4361 users, as well as future IBM 9370 users.

In other words, 9370 did not have extended addressing architecture. Which is what you said all along. A problem with the table is that it refers to processors by 'series' based on the most advanced architecture supported; but this isn't how they were sold. (Though it is more or less how we viewed them. "That's an XA machine.") Anyway, it sounds like you're on top of things here. Trevor Hanson 21:57, 16 November 2006 (UTC)

Yes and no.. The problem (and it's not the first time I've seen these discussions) is that the term S/370 is ambiguous ! it refers to both a technology (for example, S/360 differs from S/370 by the memory technology) and an architecture (S/370 : 24 bit, channel/CU/device addressing based I/O Architecture - XA : 31 bit, Subchannel based I/O architecture)... It is possible that the 9370 may *not* be considered a S/370 technology machine although it ran exclusively the S/370 architecture (hence the much debated "S/370 compatible" discussion above).. Considering some transition machines ran *both* architectures - the boundary is very hard to determine.. Therefore, I am considering moving the 9370 to the "S/370 Compatible" category... how does that sound ? Ivan Scott Warren 22:10, 16 November 2006 (UTC)

Looks good...or as good as it can look given the presence of the strange "S/370-compatible" nomenclature. (Thank you, IBM.) Does it make sense to list the 4381 and 3090 as having "extended real addressing" since they were ESA-capable? To my mind, that special category is just for those few >16Mb machines that were available before XA. Trevor Hanson 05:41, 17 November 2006 (UTC)

I think it does make sense because the 308x, the 4381 and the 3090 were machines that could address more than 16MB when configured to run in S/370 architecture mode. This 'extended real addressing' feature is a S/370 only feature control that allowed overcoming the 16MB real storage limit by using a DAT mode trick (by using a couple of bits in the PTEs) and this is not related to XA or ESA (Principle of Operations wise). The fact that the 3081, 4381 and 3090 were XA capable (meaning they could be configured to run in XA or ESA architectural mode) is quite a different matter. The fact is, I'm not even sure the 303X could address more than 16MB - and if this is the case, all S/370 extended real addressing machines would be also XA capable machines. Ivan Scott Warren 22:57, 20 November 2006 (UTC)

I'm pretty sure the 3031 could not, and fairly sure the 3032 could not, but I do know for a fact that the 3033 could address more than 16 MB of real storage: one shop I worked at had a 3033 with 32 MB real. Jay Maynard 02:36, 21 November 2006 (UTC)

*** new comments follow

Extended real addressing definitely predated XA. See the Padegs paper System/370 Extended Architecture: design considerations (http://www.research.ibm.com/journal/rd/255/ibmrd2703B.pdf). He talks about "...the introduction of the extended-real-addressing facility, first shipped in October 1981 on the 3033 and 3081 processors" and says: "Most 370-XA facilities were made generally available earlier this year (as of the date of this publication [1983]) on the 3081 and 3083 machines." In other words, XRA (or whatever acronym was used) was available from 1981-83, on 3033, 3081, and unspecified other processors, until XA was made available in 1983. (And that's the sequence of events I remember. I too saw 3033 systems with >16Mb.)

Your (ISW's) point about accessing more than 16MB in S/370 mode is a good one. I was originally classifying the systems based on when they were released, relative to the interval before XA in 1983 – when XRA was the only game in town for large real memory. But as you point out, non-XA installations after 1983 were also using this capability. So I agree: leave it in.

We could use some release notes from the period or something, to clarify which capabilities were on which processors. Though I guess at the end of the day its just us three dinosaurs who care. :) And we can't come up with the answer anyway. Trevor Hanson 05:37, 21 November 2006 (UTC)

[edit] Added architecture chapter

I just added a chapter (attempting) to make a description of the S/370 architecture itself. Could Trevor or Jay (or whoever) cross read it for me, add possible links to defined terms, etc, etc.. (I am not an expert in wikipedia matter so this chapter probably needs some editing !) Ivan Scott Warren 23:48, 23 November 2006 (UTC)

A very nice addition. It strikes me as having the right level of detail versus overview material. I'm quite happy with it. If I see some minor formatting/wikification edits, I'll stick my oar in.

I do see one point that might be made earlier and more strongly: the relationship between S/370 P.O.O. and its predecessor, the S/360 P.O.O., and the practical importance of both those documents. The S/370 manual is footnoted, and the backward-compatibility point is made at the end of the section, but this issue strikes me as fundamental to the S/360-370-390-etc. family. The S/370 architecture wasn't cooked up in a vacuum. I was still using a S/360-67 green card in the 90s, and that strikes me as remarkable.

Anyway, a nice improvement. Trevor Hanson 20:03, 24 November 2006 (UTC)

Thanks ! As suggested, I added a more detailed explanation in the chapter header about the evolution from S/360 to S/370. Ivan Scott Warren 23:02, 25 November 2006 (UTC)

Should most of the architecture stuff go into the System/360 page, if it's not there already, with the S/370 architecture stuff describing what stuff changed or was added between S/360 and S/370? Guy Harris 08:48, 10 December 2006 (UTC)

[edit] Violations of backward compatibility

Can anybody come up with some examples of S/360 problem state functionality that went away with the S/370? I'd like to be able to say that, from the standpoint of application programs coded in assembler, there were no violations of backward compatibility. However, I have the nagging memory of a few little things changing. Maybe some of the packed decimal instructions? (I never had to use them much anyway.) I understand why we changed the description to "mostly backward compatible" but I don't think today's programmers realize how much consistency was preserved through the entire product family. I think it would be good to get precise about this. Obviously there were lots of changes moving forward, especially in super state, but an awful lot of old code continued to run without modification. Trevor Hanson 06:18, 4 December 2006 (UTC)

The only change I know of that was visible in problem state was the ASCII mode bit in the PSW, which changed how the decimal instructions behaved in a subtle way. (IIRC, it changed the high order nibble of decimal values generated by the processor from X'F' to X'B'.) That turned out to not get used very much at all, and they removed that function in S/370, changing the meaning of the PSW bit to signal that the CPU was in extended mode. The authoritative answer will be found in the S/360 compatibility section of the S/370 POO. Jay Maynard 11:57, 4 December 2006 (UTC)

By the way, do we have a generic name for the S/360-S/370-S/390 instruction architecture family (analogous to "x86")? I'd really like to have a convenient name for the class of systems that have run (for example) the VM family or the OS family. It seems stupid to just say "IBM mainframe" (since one might obviously consider 70xx systems in that group, or any huge IBM systems regardless of architecture) – and I hate just giving a list of all the different product lines, especially those with a 'z' in them. Trevor Hanson 06:18, 4 December 2006 (UTC)

Were it not for the z/Architecture, you could call it System/3x0, I guess (by analogy to x86 - whose analog to z/Architecture, namely x86-64, is still part of x86). Guy Harris 08:50, 10 December 2006 (UTC)