PDP-11 Memory

[Bill Gunshannon]

On 1/12/19 1:13 PM, Jerry Weiss wrote:
> On 1/12/19 11:39 AM, Bill Gunshannon via cctalk wrote:
>> On 1/12/19 12:29 PM, Pete Turnbull via cctalk wrote:
>>> On 12/01/2019 01:24, Zane Healy via cctalk wrote:
>>>
>>>> I’m pretty sure you could get the /23+, /53, /73, /83, and /93 in
>>>> either a BA23 or a BA123.  I have an actual badged BA23 pedestal for
>>>> my /23+.
>>> I'm fairly certain all microPDP-11/23+ systems were only sold in BA23
>>> boxes, and I think microPDP-11/73 and the later, cheaper, cut-down 11/53
>>> were as well.  But almost all the 11/83 systems I've ever seen were in
>>> BA123 boxes, though they did sell some in BA23 pedestals - I've got one.
>>>
>> One confusing part of this.  Everything I have read today
>> seems to say that the only difference between the 11/73
>> and the 11/83 in a MicroPDP-11 was the memory used.
>> QBUS = 11/73
>> PMI = 11/83
>>
> I use this guide in general - 
> http://web.frainresearch.org:8080/projects/pdp-11/dcj11.php to 
> understand the key differences in DEC DCJ11 implementations. You can see 
> how the clock speed, caching and memory type drove differences in 
> performance and marketing labels.
> 
> The 11/83 (M8190-AD or AE) with Non-PMI memory is just a slow 11/83 in 
> my view. I know RT11 did report it as an 11/73.   It could be that from 
> a software perspective, RT11 might not be possible to determine the 
> actual module in use.

I always thought it was an 11/73.  It wasn't until the last few days
that I saw the difference mentioned.  It works fine as an 11/73 and
having PMI memory and making it an 11/83 would just be for fun anyway.
I have run Ultrix-11 on 11/73's with no real problems.

> 
> Does the 2MB 11/93 not work with and extra 2Mb of QBUS Non-PMI memory?  
> I would have thought the upper 2MB would still be addressable, if for 
> nothing else than for compatibility memory mapped display controllers 
> and such.

I had tried it and, no, it didn't work.  I then had people tell me
it wouldn't.  I have also been told the only way to upgrade is to
add the missing memory onto the CPU board.  I find that hard to
believe, but I suppose it is possible.  I am not sure I could do
that upgrade as some of the chips are surface mount.  Not that it
matters as a search could not turn up any supply for those particular
memory chips.  But, if I came up with a 2 meg or pair of 1 meg PMI
boards I would definitely try it.  :-)  Just like the 11/73|11/83
deal.  If a 4 meg PMI card fell in my lap I would definitely try
it to see if there was a difference.  Matter of fact, I would likely
find some benchmarks I could run under Ultrix-11 and see what the
actual difference was.  But, it's all academic cause I really don't
see any PMI memory falling from the sky and I haven't seen any pigs
fly by lately.  :-)

bill