sml@wdl1.UUCP (05/29/84)
#R:rlgvax:-195500:wdl1:5900006:000:1858 wdl1!sml May 29 15:08:00 1984 In response to Guy Harris' critique of my comments on the PDP-9: > Except, of course, for the word size, since the 8 had 12-bit words > and the 9 had 18-bit words. And except for the instruction set, which > was different... The architectures of the PDP-8 and PDP-9 are quite similar. The instruction set is essentially the same (although I'm sure the numeric op codes are different). I learned assembler for the PDP-9 by reading Dec's "Introduction to Programming" (I might not have this name exactly correct) book which describes the PDP-8. The differences between the two machines were easy to assimulate. (Note: the utility software described is different. The assembly language is what's essentially identical between the two machines.) > Well, since the PDP-15 came out as a successor to the PDP-9, either the > PDP-9 didn't have an assembler until the PDP-15 came out or the PDP-15 > assembler was made out of the PDP-9 assembler (a little more likely). I referred to the Dectape based OS which was retrofitted to the 9 from the 15. (Actually the 15's system was written for a disk. It was then backed down to Dectape. One could even do overlays using Dectape. Overlaid programs were entertaining to watch.) Before this the 9 had a paper tape based assembler, Fortran compiler, and other goodies. One of Dec's requirements for software written for the 15 was that it be usable on the 9. This resulted in things such as fortran not using the 15's index registers since these were unavailable on the 9. > (BTW, I was very surprised when I read between the lines of some PDP-9 > book and found out that the PDP-9 was microprogrammed...) That's at least one correct fact. I was quite proud of myself when I invented my own instruction for the extended arithmetic element. Steve Lazarus Ford Aerospace ...fortune!wdl1 sml@ford-wdl1