🚀 go-pugleaf

[I think that most of us agree that Multics was great.  Let's finish up with
 Multics and move on to what we should put into present-day OS's -DL]

Well, actually, I expect you've been reading the Organick book.  Originally
Multics used 64K (2**16) word segments, but for a long time they've been
(an inconvenient) 2**18 - 1K word segments.  The missing 1K is interesting.

The original processor was architecturally more-or-less a copy of IBM
7094 type machines.  (GE-645).  The bits needed to do most of the fancy
character operations, most of the segmentation and paging support, and
the 8-ring protection, are in an add-on box tacked onto the standard (GCOS
system type) processor.  Whoever designed that box used page number 0 as
a special case, so that segments could only be 1-255 (1K) pages long.
Most of the standard hardware, bar the tack-on Multics box, could cope
with 256K segments.  The character-handling instructions and some others
can't.

Recently work has been done to allow 'large segments' -- that is, things
which are more than one segment long but which can be manipulated, at least
from highe-level languages, as though they were normal segments.

The original development was done by AT&T (Bell Labs), General Electric, and
MIT, sponsored by the US DoD.  AT&T pulled out fairly early.  Then (mid-60s, I
think, maybe early 70s) GE sold out to Honeywell.  HIS produced several
newer versions of GCOS hardware (though mostly the same architecture, just
faster/denser parts) with tack-on Multics boxes.

The real problem with Multics was that there was never a processor designed
to run it.  It was always a bodge-box attached to a non-Multics processor.
HIS wouldn't develop new hardware because Multics didn't sell well enough.
Multics didn't sell well enough because many if not most of the HIS sales
staff didn't even know about it.  There were incredible political rows about
this within HIS, but it appears to me that there were 2 factors involved:
(1) HIS marketing regarded Multics primarily as a research project -- an
attitude not fought by the developers, particularly; and (2) most of the
higher-level executives at a few critical moments had strong past attachments
to the GCOS side of the product line, and saw Multics as an internal
competitor.

Still, it lives on in the form of influences to a number of O/Ss which
acknowledge a debt to it -- the first 2 to come to mind are U*ix and Primos.