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--- systems:pdp7_unix [2015/12/30 00:04] – wkt
+++ systems:pdp7_unix [2015/12/30 00:09] – wkt
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 In October 2009, Dennis sent Warren Toomey a private e-mail that said "In other news, I have found the book that has the [PDP-7] listings that I knew I had, that of (some) of the user-level commands. I wonder what's the best way to get it scanned?". Unfortunately, Dennis passed away before he could get the listings scanned in.
+===== PDP-9 Unix =====
+In several places, including the [[http://www.tuhs.org/Archive/Documentation/Papers/unix_cacm74.pdf|CACM paper]], there is mention made of Unix running on a PDP-9. Dennis Ritchie posted [[http://minnie.tuhs.org/pipermail/pups/2002-August/000529.html|a message on the PUPS mailing list]] in August 2002 which said:
+The [PDP-]7, 9, 15 were very compatible.  I think the -15 had some scheme for using an index register, which the earlier ones didn't have, but it was otherwise pretty much identical in IS architecture.
+There was very little rewriting to try Unix out on the -9 and -15; perhaps just some tweaks in
+the disk device commands.  I don't think the system actually ran on either for more than a few hours. Ken was just playing around.
+The -15 may have had an electrically different bus, but I'm reasonably sure it was not a Unibus. All of them used IOT instructions, not memory-mapped IO registers.
+Both of the machines we tried were being used by other groups and we couldn't squat on them as with the PDP-7. I recall that  the -15's main job was controlling a step-and-repeat camera that exposed LSI masks.