[Simh] pdp11 i/o addressing

[Ethan Dicks]

On Fri, Feb 16, 2018 at 10:44 AM, Mike Stramba <mikestramba at gmail.com> wrote:
> Thanks Guys.
>
> I *had* downloaded a handbook... but it was the *oldest* one (1969)
> ;),  hence no mention of virtual memory in it ;)

Yeah, Once you get to anything with an 18-bit Unibus, there's a distinction.

What's sometimes hard to get used to is for the PDP-11, virtual space
is *smaller* than physical space.  Virtual space is 64K.  Physical
space can be up to 4MB depending on the model.

I started on a VAX with 2MB of physical memory in a 16MB physical
address space but with 4GB virtual addresses.  Switching over to the
PDP-11 was odd from that.

-ethan