Reproducing old machines with newer technology (Re: PDP-12 at the RICM)

One possible answer is ?because I can?. As for whether it accurately reflects the details of the real thing, that depends. Not the peripherals, of course. If the peripherals are much more interesting than the CPU, I agree there isn?t much point. In the case of machines like the CDC 6600, the CPU is very interesting, the PPUs also, some of the peripheral controllers to some extent, but the peripheral devices themselves are not interesting at all. An FPGA model can reproduce the interesting parts. The accuracy of the FPGA depends on the approach. If it?s a structural (gate level) model, it is as accurate as the schematics you?re working from. And as I mentioned, that accuracy is quite good; it lets you see obscure details that are not documented and certainly not visible in a software simulator. The example I like to point to is the 6000 property that you can figure out a PPU 0 hard loop by doing a deadstart dump and looking for an unexpected zero in the instruction area: deadstart writes a zero where the P register points at that time. But you won?t find that documented or explained anywhere. The FPGA model derived from the schematics reproduces this behavior, and when you look at how it happens, the explanation becomes blindingly obvious. *This* is why I feel there?s a point in doing this sort of work. paul