[Simh] The Missing PDP-8s

[Bob Supnik]

Well, no. It's a PDP-8/A as initially released and documented in the 
late 1976 PDP-8/A manuals and schematics. That machine was limited to 
32KW. So was the initial, 1976 version of the FPP8-A.

The KT8-A was released in mid 1978. It expanded memory capability to 
128KW and added a number of other interesting features. It wouldn't be 
that hard to add it.

The 8/A was not the end of the line, of course. The Intersil 6100 and 
Harris 6120 took the PDP8 into VLSI and added additional features.

I'm not sure where I'd draw the line between static and dynamic 
compilation of models. Different simulators have taken different approaches:

- The PDP11 allows the model to be set dynamically, except for the UC15.
- The VAX requires the model to be compiled statically (every VAX model 
is a different simulator).
- The PDP10 requires the model to be compiled statically, but the type 
of memory management can be selected dynamically on the KS10.
- The 18b PDPs require different models to be compiled statically, but 
the type of memory management can be selected dynamically on the PDP9 
and PDP15.

I don't think it's impossible to make a dynamic 'all-in-one' PDP8 CPU. 
You'd have to identify how the earlier machines handled 'unpredictable' 
results, e.g., RTL!RTR, but working examples of every PDP8 (not the 
PDP5, though) are still extant if questions need to be answered. IO is 
uglier. The PDP5 and classic PDP8 used peripherals similar to the PDP4 
and PDP7, like the type 552 magtape and type 555 DECtape controllers. 
Starting with the 8/I, we see the "modern" form of storage controllers. 
However, the 8/I still uses the older type 645 line printer controller 
instead of the newer LP8E/LP8A. The serial drums from the classic 8 made 
it to the 8/I but were superseded by the DF32 and then the RF08. 
Real-time clock programming is very different from the old models to the 
new ones. Etc, etc, and so forth.



On 8/13/2019 3:51 PM, Warren Young <tangentsoft at gmail.com> wrote:
> It's a mongrel. SIMH's FPP (floating point processor) peripheral emulates
> the version for the 8/a, but memory is limited to 32 kWords as in all
> models before the 8/a, which added a mode to allow 128 kWords of core or
> semiconductor RAM.