Anyone got a PACE system? Or software, docs?

Eric Smith eric at
Wed May 13 01:52:12 CDT 2009

I'm interested in talking to anyone who has or had a National 
Semiconductor PACE or INS8900 system, or documentation or software for one.

In order to have something halfway interesting to run on the homebrew 
IMP-16 system John List designed and built, I decided to start from PACE 
software, since the PACE architecture is derived from (but not 
binary-compatible with) the IMP-16, which itself was inspired by the 
Data General Nova.

A few years ago a friend gave me a copy of the fig-FORTH listing for the 
PACE, which turned out to be missing a page.  The listing is on 
Bitsavers, but a complete listing is now available on the fig-FORTH 
implementations page on

Over the course of the last week, I typed in the fig-FORTH listing (both 
source and object code), wrote a PACE cross-assembler, assembled 
fig-FORTH and compared the generated object to what I typed in, fixed 
the errors, wrote a PACE simulator, and fixed the fatal bug in the "U/" 
word of the fig-FORTH listing.  (Maybe no one other than the author ever 
actually ran PACE fig-FORTH?)  Now that it's working I've just started 
trying to translate it for the IMP-16, which doesn't have the RADC and 
SUBB instructions of the PACE, and which has somewhat different shift, 
rotate, and flag instructions.

Google doesn't turn up much about the PACE other than the few manuals 
and datasheets already on Bitsavers.  I know that a paper tape based 
resident assembler existed, as well as a disk operating system with a 
resident assembler.  There may have also been a BASIC interpreter.


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