Newsgroups: comp.arch Path: utzoo!henry From: henry@utzoo.uucp (Henry Spencer) Subject: Re: Instruction (dis)continuation Message-ID: <1989Sep7.164230.21570@utzoo.uucp> Organization: U of Toronto Zoology References: <1989Aug24.215104.156@mentor.com> <231@ssp1.idca.tds.philips.nl> <2345@oakhill.UUCP> <204@bbxeng.UUCP> <5990@pt.cs.cmu.edu> <205@bbxeng.UUCP> <44908@bbn.COM> <2812@masscomp.UUCP> <4008@bd.sei.cmu.edu> Date: Thu, 7 Sep 89 16:42:30 GMT In article <4008@bd.sei.cmu.edu> firth@sei.cmu.edu (Robert Firth) writes: >>... I seem to recall they solved it by having a diagnostic >>register in which the CPU wrote which registers had been incremented or >>decremented and by how much. > >>Some PDP-11s had this register, some did not... > >The handbooks tell me that this register was implemented on all but one >of the memory-managed PDP-11s... Unfortunately, not so: your handbooks probably are not complete. The register appeared on the 45, the first memory-managed 11. It was left out on the 40, the second. The 40's MMU was a cut-down version of the rather kitchen-sink 45 design, since the 40 was a lower-cost machine, but unfortunately they left out a couple of important things because no DEC software of the time used them. (The changed-registers register was one, split-space was the other.) The larger memory-managed 11s followed the 45; the smaller ones followed the 40. The 40, 34, 60, 23, and 24, at least, had the brain-damaged MMU. The 50, 55, and 70 had the 45 MMU, but that was no big trick since they were all 45s with changes in memory subsystem details. The 44 had a *slightly* simplified 45 MMU that got rid of some of the silliness but left everything important in. I think the more recent 11s have mostly followed the 44, but I haven't been keeping track. -- V7 /bin/mail source: 554 lines.| Henry Spencer at U of Toronto Zoology 1989 X.400 specs: 2200+ pages. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu