just double checking, in case the odd.html had a typo: it was a KS11, not a KT11-B? Is there any chance there was an error in recollection? ron On Sat, Jun 22, 2019 at 11:18 AM Noel Chiappa <jnc(a)mercury.lcs.mit.edu> wrote: > > This is an appeal to the few really-old-timers (i.e. who used the PDP-11/20 > version of Unix) on the list to see if they remember _anything_ of the KS11 > memory mapping unit used on that machine. > > Next to nothing is known of the KS11. Dennis' page "Odd Comments and Strange > Doings in Unix": > > https://www.bell-labs.com/usr/dmr/www/odd.html > > has a story involving it (at the end), and that is all I've ever been able > to find out about it. > > I don't expect documentation, but I am hoping someone will remember > _basically_ what it did. My original guess as to its functionality, from that > page, was that it's not part of the CPU, but a UNIBUS device, placed between > the UNIBUS leaving the CPU, and the rest of the the bus, which perhaps mapped > addresses around (and definitely limited user access to I/O page addresses). > > It might also have mapped part of the UNIBUS space which the -11/20 CPU _can_ > see (i.e. in the 0-56KB range) up to UNIBUS higher addresses, where 'extra' > memory is configured - but that's just a guess; but it is an example of the > kind of info I'd like to find out about it - just the briefest of high-level > descriptions would be an improvement on what little we have now! > > On re-reading that page, I see it apparently supported some sort of > user/kernel mode distinction, which might have require a tie-in to the > CPU. (But not necessarily; if there was a flop in the KS11 which stored the > 'CPU mode' bit, it might be automatically cleared on all interrupts. Not sure > how it would have handled traps, though.) > > Even extremely dim memories will be an improvement on the blank canvas we > have now! > > Noel