VAXen and minimal memory (was Re: The PDP11/04 has landed..)

Ethan Dicks ethan.dicks at
Mon Feb 8 21:57:16 CST 2016

On Mon, Feb 8, 2016 at 9:48 PM, Jon Elson <elson at> wrote:
> On 02/08/2016 03:23 PM, Ethan Dicks wrote:
>> I don't know if you could use the 256K boards (populated with 4116s) in
>> the 11/730 due to the tri-voltage 4116s, but even if they worked, you
>> wouldn't want to - 5 of them just isn't that much RAM.
> We ran our first 11/780 with 2 memory boards.  I THINK we had a total of 256
> KB, and one Friday afternoon one of them died and we had to run over the
> weekend with only one board, so that would have been 128 KB.  Yes, it was a
> bit tight on memory, but we got a LOT done on that machine.

As I mentioned our first 11/750 was delivered with 512KB (we upgraded
it pretty quickly to 8 boards for 2MB, where it ran for years).  The
11/750 first shipped with IIRC VMS 2.0.  My first encounters with VMS
was around mid-1984 and VMS 3.4.  We had 8MB of memory in our second
11/750 but it was supporting 50+ users.

That 11/750 went off-lease, we sent it back.  That's why I had to
upgrade the other one, so we'd still have an 8MB VAX in-house.  It ran
VMS 4.7 at the end of its days 23 years ago (we had quite a bit of
software that wasn't available for/wasn't licensed for/wasn't under
paid-maintenance for 5.x).  I haven't powered it up since we left that
building (I do occasionally power up the 8300 that we got for product

So I'm fairly confident that 512MB is enough for VMS 2.0 but I _think_
by 3.0, you had to have a megabyte or two.  1.25MB would be the most
you could stuff in a 11/730 if you could use the boards populated with
16Kbit DRAMs.  I don't think VMS 2.x runs on an 11/730 (but I could be
wrong there).  We ran Ultrix 1.1 and VMS 5.0 on one of ours (with
5MB).  VMS 5.0 barely fit - we mostly used that to link our product
binaries under 5.x for distribution to our customers.

I do know someone in Ohio who ran VMS 5.0 on a VAX-11/725, but they
did it by cutting a slot in the skin and running a BC11 cable out to a
BA11 box next to the 11/725 and stuffing a UDA50 in the BA11.  With an
external disk, there's no practical difference between an 11/725 and
an 11/730... same CPU, same backplane, same memory... just a packaging


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