Antonio Carlini a.carlini at
Wed May 1 14:54:41 CDT 2019

On 30/04/2019 10:25, Huw Davies via cctalk wrote:

> I know later 780s (probably with an upgraded memory controller) supported 64MB of memory.
> I have used VMS 1.6 and started managing VMS systems around the 2.4 timeframe.
> I haven’t looked but does the simh 11/780 also provide PDP-11 compatibility mode? You used to run a very large amount of -11 code in VMS 1.x..

I may have missed some of the thread, so this might be old news ...

The VAX-11/780 was followed by the VAX-11/750 and that needed (iirc) VMS 

The VAX-11/730 was next and that needed VMS V3.0.

Then (I think) came the VAX 8600 and that needed VMS V4.0. That (I 
think, but I can't find anything to support this right now ...) is when 
the last of the PDP-11 compatibility code was finally removed.

So I think that to use anything pre-V4.0 you need compatibility mode 
support in SIMH. But that seems to be there.

I've not used anything older than V3.x ... I remember command line 
recall arriving, so I expect that happened in V4.0.

I would expect V1.x to feel distinctly clunky in comparison ... to V4.x 
and later.

Still a fun exercise though I would think.


Antonio Carlini
antonio at

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