Re: [TUHS] Any oldtimers remember anything about the KS11 on the -11/20?

[ron minnich <rminnich@gmail.com>]

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@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