RL02 version of UNIX6?

[Paul Koning]

> On Feb 3, 2017, at 3:25 PM, william degnan <billdegnan at gmail.com> wrote:
> 
> On Fri, Feb 3, 2017 at 2:31 PM, Paul Koning <paulkoning at comcast.net> wrote:
> 
>> 
>>> On Feb 3, 2017, at 12:00 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu>
>> wrote:
>>> 
>>>> From: Paul Koning
>>> 
>>>> Another OS that would run on your machine (as well as an 11/20) would
>>>> be RSTS-11 (V4, or I suppose V3 if you can find that)
>>> 
>>> I'd love to have an old RSTS-11, is there any variant around?
>> 
>> Yes, on bitsavers.  But John's comment reminds me that RSTS-11 V4A doesn't
>> support RL02.  (Only RF11, RK11, RP11.)  V4B may be different, I don't know.
>> 
>>>> didn't use the MMU
>>> 
>>> Huh? He's got an MMU (I think): it's the EIS he's currently struggling
>> with.
>> 
>> True.  I meant to point out the main difference between RSTS-11 and
>> RSTS/E.  The other difference is that it doesn't require EIS.  Both follow
>> from the fact it was designed for the 11/20.
>> 
>>        paul
>> 
>> 
> So you're saying for a system with a MMU but no working EIS (removed for
> now) and 64KW RAM (half populated M7891) you're suggesting which OS?  I
> still have to research the best options, RSX-11M?

I'm not sure there is one.  DEC OS designers typically would assume that they are dealing with non-broken systems.  Systems with MMU all have EIS, so an OS that requires an MMU would typically take advantage of EIS instructions.  That's the case in RSTS/E, for example.

OSs designed for non-MMU systems would also typically assume no EIS, because they were intended for the entire PDP-11 family including 11/20 and the like.

In other words, if you don't have an EIS that works, you're likely to be limited to no-MMU systems because those are likely to be the only ones whose authors avoided EIS instructions.

There may be some mixed cases, an OS where the same basic system can be built for no-MMU as well as MMU configs.  If so, there might be a way to build an MMU=yes, EIS=no config.  Or it may come with EIS=no by default because some of its configs have to handle that and it's easier to do it consistenly.  Possibly RSX is such an OS; I don't know.  

	paul