[Simh] EXT :Re: VAX/VMS

[Hittner, David T (IS)]

This is the beauty of the SIMH VAX and VAX780. The simulators allow running much larger resource capacities than were affordable at the time. And run it faster.

While it is possible to run VMS 7.3 on the resource constrained 11/725, 11/730, MicroVAX I, and MicroVAX 2000 systems, the challenge is getting it there in the first place. Memory limits can be addressed by SYSGEN tweaks, disk limits can be addressed by installation tailoring and having multiple or external disks, but it's still hard to load the OS on resource-constrained hardware.

My company bought one of the backplane-epoxied MicroVAX I's to "double" the processing power of our production 11/730, by getting the programmers and our "damn compiler runs" off of the main production system. This MicroVAX I system was extremely resource-limited with 2MB memory and a 31MB disk drive. But it ran VMS well enough for two programmers.  When the MicroVAX II came along, the 11/730 was replaced and moved from the shop floor to the office space. This allowed us to upgrade the file transfer between the systems from serial Kermit to always-up Asynchronous DECnet. When the programmers complained about the relative speed of the MicroVAX I vs. the MicroVAX II, the MicroVAX I got a few upgrades: an un-epoxied backplane to allow more boards, an RQDX3/RD54 controller/disk combination, and the maximum 4MB memory. Eventually, it was upgraded to a MicroVAX II board and memory, and an Ethernet controller was added to both systems to allow a small VAXCluster as incremental funding became available.

As a Digital VAR, my company always faced the resource-constrained limits when selling. Most manufacturing companies buying our package couldn't afford really good systems, and settled for resource-constrained versions.

Dave

-----Original Message-----
From: Simh [mailto:simh-bounces at trailing-edge.com] On Behalf Of Ethan Dicks
Sent: Tuesday, February 16, 2016 2:18 AM
To: simh at trailing-edge.com
Subject: EXT :Re: [Simh] VAX/VMS

On Tue, Feb 16, 2016 at 1:57 AM, Wilm Boerhout <wboerhout at gmail.com> wrote:
> More precisely, V7.3 will run on *any* VAX, including the primal VAX-11/780.
> This level of backwards compatibility is unique.

I'm sure 7.3 has a very broad list of what it runs on, but (considering I own the hardware in question), does it run on the smallest of the small?  VAX-11/725?  MicroVAX 2000?  In the case of the 11/725 (and the 11/730), minimum memory requirements come to mind.
They are limited to 5MB (the MicroVAX 2000 can take far more memory than that and is not a problem there)  The 11/725, by default, comes with the RC25 as its disk, but you can stick a different disk controller on the Unibus (a SCSI controller does nicely if you can find an affordable one, but an SMD controller is easier to locate), and I do know someone who did some sheetmetal cutting and added an external BA11 to their 11/725 where they could put any number of Unibus disk interfaces.  In the case of the MicroVAX 2000, it's a busless design and comes with the equivalent of an RQDX3, so is limited to one internal RD54 and one external RD54, though you could give it a go to MOP boot it via Ethernet.  The MicroVAX I also has its place on the small end, with Qbus memory and 4MB max, but at least you can toss a Qbus SCSI controller in one and not suffer with the limitations of its RQDX1.

So if 7.3 fits on a ~150MB disk and in 4MB or 5MB of RAM, it'll fit on any of these except perhaps an unexpanded 11/725 (but to be fair, not much fit on an RC25, even when it _was_ on the supported list).

I'm not decrying 7.3 at all, but having tried to shoehorn 6.2 on a standard MicroVAX II (9MB RAM, 154MB RD54), I do wonder about the small, hardware-constrained machines.  For my own collection, I tend to run whatever was common in the day for that specific hardware, anywhere from MicroVMS 4.whatever through VMS 4.7 through VMS 5.5 or so.  Again, nothing wrong with 6.x or 7.x if you have memory and disk to handle it, but not having some of the more expandable models, I didn't do much with the more recent versions and the VAX (but plenty with more recent versions and Alpha.  Talk about needing more RAM!)

-ethan
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