[Simh] VAX/VMS

[Ethan Dicks]

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