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

Chuck Guzis cclist at
Tue Jul 14 12:17:20 CDT 2015

I'm missing something in this discussion, I think.

HDL's (take your pick) are just programming languages like FORTRAN or C 
with different constraints.  What's the point of going to all the 
trouble of doing an FPGA implementation of a slow old architecture, when 
pretty much the same result could be obtained by running a software 
emulator?  Neither accurately reflects the details of the real 
thing--and there will always be the aspect of missing peripherals.

Perhaps the worst aspect of using FPGA is that this is a rapidly moving 
field, so that the part you used to do your implementation 10 years ago 
will no longer be available.    I've done a few designs using 5V CPLDs 
(XC95xx series) not *that* long ago.  Now they themselves are quaint 
examples of obsolete hardware.  You can't win.

You can move software-only simulators quite easily, but I'm not as 
sanguine about FPGA designs.

And you still don't have the peripherals.  I suppose one could emulate a 
Univac Solid State machine in FPGA, but what would one do about the 
all-important drum coupled to the card reader and printer.  Has anyone 
rolled out a design for a DIY 1403 printer?

I've run the Cyber emulator as well as various SIMH emulators from time 
to time, but it's just not the same as the real thing--it's not even 
remotely the same.


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