PDP-12 Restoration at the RICM

[Jon Elson]

On 05/13/2015 08:37 PM, Eric Smith wrote:
> >From the web page:
>      "so it actually has two processors"
>
> Is that true? I haven't had time to make a detailed study of the
> PDP-12 logic design, but my understanding was that unlike the LINC-8,
> which basically was two separate processors mashed together, the
> PDP-12 was a single integrated processor with two modes (PDP-8 and
> LINC). I was told that there were some commonalities that were taken
> advantage of, such that merging it resulted in reduction of the total
> logic necessary as compared to the LINC-8.
>
I'm pretty sure this is true, the amount of logic in the 
machine is not that much more than similar 12-bit CPUs.
The ALU had to handle both ones-complement and two's 
complement operations, and the instruction decode logic 
needed to be about double, but the data paths logic could 
all be done with one implementation.

I did use the PDP-12 at Washington University, and it was a 
real nice machine!

Jon