🚀 go-pugleaf

On Sat, 11 Aug 2018 15:23:07 -0000 (UTC), John Levine <jo...@taugh.com> wrote:
>In article <1173318279.555679658.757...@news.eternal-september.org>,
>Peter Flass  <peter...@yahoo.com> wrote:
>>Yes, I loved the -10 too, although I didn't program it extensively. I was
>>sorry when it was canceled, although I suspect it would have been difficult
>>to expand the architecture to larger memory sizes.
>
>We don't have to guess.  They did expand the addressing for the DEC-20
>and it was pretty ugly.  The extra address bits were called the
>section number, with some addressing being within the current section
>and some being global.  TOPS-20 supported it but I don't recall many
>programs using it.

It wasn't that ugly, IMO, but I never really tried to use it myself.

TOPS-20 itself used it, but without looking at my references (currently in
boxes) I cannot recall the exact details.  If memory serves, most or all monitor
code was in section zero; a couple of non-zero sections were used for data
and/or buffers.

1022 (database program) would have been an obvious candidate for using sections,
and I think it might have.  (I've cross-posted this to alt.sys.pdp10.)

I think that any reasonably coded programs of the day would have fit in section
zero, with non-zero sections used for data.  Given a good design one might not
have to actually move data in order to process it -- just change the memory map
tables with the appropriate system calls.

One thing on my todo list that I never tried was to see if the PMAP bug also
applied to SMAP.  (PMAP page A to page B; PMAP page B to page A.  Any reference
to either page causes the microcode to loop forever trying to resolve the
address.  When the front-end PDP-11 fails to get any response from the PDP-10
after a certain interval, it generates a "keep alive" halt and forces a reboot.)

I can't even remember how many bits in an extended address, so I'm not sure how
well it would work given today's memory sizes.  One must remember that PDP-10
addresses point to 36-bit words, not 8-bit bytes.