7 Feb
2026
7 Feb
'26
12:21 a.m.
VM included CP and CMS. CP ran on the hardware and created virtual
machines. CMS ran in a virtual machine and intereacted with users, but
could not run on the real hardware (though the very early versions
purportedly could). native timesharing and batch jobs each run under CMS
on a virtual machine
BUT, in the virtual machines, you could also run...
--DOS/VS the operating system that ran on the smaller IBM mainframes
--OS/VS1 the operating system that ran on mid-range hardware, similar to
what ran on larger system 360 machines, with one continuous virtual storage
--OS/VS2 which ran on largest hardware, each user or batch job got the same
address range
--VM/370....which could again run all of the above
...as deep as you wanted. somebody got a system to IPL (boot) like 20-some
levels deep. it got slower and slower each level you went, of course as
everything got paged in and out to do anything.
the instruction to store the cpu id was modified in a virtual machine to
put a hex FF in the last byte because otherwise there was NO WAY to tell if
you were running on real hardware or in a virtual job under CP, other than
a timing loop.
this is why i am dissatisfied with virtualization on intel hardware. to
many things DO NOT WORK unless the hypervisor knows it has to fake
something to make the virtual machine work, and i cannot do a base install
in a virtual machine of any random install media
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On Fri, Feb 6, 2026 at 10:12 PM Wayne S via cctalk <cctalk(a)classiccmp.org>
wrote:
Stuff i’m kinda remembering now.
CMS was an acronym for Conversational Monitor System.
You could write short programs using a scripting language, i think it was
called REXX.
Sent from my iPhone
--
--Carey
On Feb 6, 2026, at 20:00, Wayne S
<wayne.sudol(a)hotmail.com> wrote:
You could run different jobs at the same time in different partitions.
Just had to make sure the jobs didn’t need the same resources or you would
get a lock. So if a jobs needed a certain tape, make sure another job
running in another partition didn’t need it.
Sent from my iPhone
> On Feb 6, 2026, at 19:51, Steve Lewis via cctalk <cctalk(a)classiccmp.org>
wrote:
>
> Dave,
>
> Page 439 of that document you linked has a nice chart of "integrated
> emulators that run execute under VM/370" - now I do recall one of the
> "famous" things about the prior S/360 was it could emulate 1401 and
other
> IBM systems. Then later on, more systems to
emulate would be the
> 709-series. Ok, so VM/370 is more like what we might today call a
> Hypervisor? So the "it looks like whatever you want" comment makes
> sense.
>
> I suppose what I'm after is more a visual on the usage of CMS, DOS/VS or
> OS/VS1 ( OS's that one would only use on an S/370 ? )
>
> I put a couple reference images here on what I have about CTSS and
TOPS-10
> (CTSS is from a modern-day emulators, TOPS-10
is from one of their
manuals
> so its from in 1970). I see how you mean
VM/370 isn't quite the same
> nature (not "just an OS" but an enterprise thing like for airlines,
banks,
> financial brokers -- and the virtualization
helped in testing/deploying
new
> systems -- that maybe had newer OS's --
without disrupting operational
> systems?)
>
> https://github.com/voidstar78/OS_NOTES
>
>
> - Steve
>
>
>
>
>>> On Fri, Feb 6, 2026 at 10:00 AM David Wade <dave.g4ugm(a)gmail.com>
wrote:
>>
>>
>>
>>> On 06/02/2026 14:55, Steve Lewis wrote:
>>> Thanks Dave, the 3270 terminal screen makes sense. Or to make use of
>>> the system and resources, you'd remote to it using a 3270.
>>> So it may have been at a time no one thought to snap a photograph of
>>> any of those 3270s in use (not just a "room full of 3270's"
kind of
>>> photo - but of the actual screen, showing whatever it was they were
>>> doing; managing tape/disk resources, files, users, or running APL or
>>> something. That's more what I was looking for, when you "used
VM/370
>>> {or remoted into it}, this is what it looked like."
>> Generally thats not what you did with VM/370. You edited, compiled, and
>> ran programs....
>>
>>>
>>> There had to be some kind of installer? Or maybe I'm viewing it wrong
>>> - they (a business) didn't just buy a S/370 then decide what OS to
>>> install. But rather it was a packaged prepared by IBM, so maybe it
>>> was pre-installed with VM/370 and configured to whatever the
>>> arrangement/contract was?
>>
>> For VM you usually got a "starter system" on a tape. There was a
>> different tape for each disk type. The first file on the tape is the
>> standalone disk dump and restore program, DDR. So you IPL (boot) from
>> this tape, and use DDR to restore the starter system to DASD (disk).
>> You usually needed three packs. The first time you IPL the restored
>> starter system it asks you some basic config questions, and you then
>> have a working system that you can use to restore the rest of the
>> VM/370, load and apply service (fixes) , and configure to your exact
>> hardware set-up.
>>
>> I expect at 522 pages this manual which covers install and congigureis
a
>> tad bigger than the one for other
systems...
>>
>>
>>
https://bitsavers.org/pdf/ibm/370/VM/370/Release_6/GC20-1801-10_VM370_Sysge…
>>
>>
>>> Or a way to say "when someone used a S/370 {or CMS}, this is what the
>>> console content looked like" (printed, or by that time yea probably
>>> more likely a CRT).
>>>
>>
>> It looked like whatever you wanted. The samples in the previous e-mail
>> are typical...
>>
>>
>>> “The Origin of the VM/370 Time-Sharing System” – R.J. Creasy gives a
>>> little bit of a description on those components CP, CMS, and RSCS.
>>> But no photo/image yet of a terminal with content to identify "yeah,
>>> see they are using a S/370 there" (maybe its listing disk packs,
>>> tapes, memory resources, etc?) I got something like this for the
>>> earlier CTSS and TOPS-10.
>>>
>> pass me what you have for that so I can see what a VM Equivalent might
>> be. The definitive thing on a users 3270 is the status bottom right
>> which on a pukka system which usually reads "VM READ VM/370" but can
>> also start "RUNNING", "HOLDING" "CP READ".
>>
>>> -Steve
>>>
>>>
>> Dave
>>