5 Jul
2016
5 Jul
'16
12:13 a.m.
QNX, which wasn't Unix compat at the time but sorta close, in the mid
1980's was very very small and ran just fine on a 80286. If my memory
serves me correctly I had 4-10 people logged into that box on terminals.
QNX, at least until they put real posix conformance in it, was a really
tiny micro kernel with the rest of the os in processes. It fit in a
4K instruction cache with room to spare.
QNX, in my opinion, is the only really interesting and commercially
proven microkernel.
On Mon, Jul 04, 2016 at 12:54:15PM -0400, Norman Wilson wrote:
Greg Lehey:
And why? Yes, the 8088 was a reasonably fast processor, so fast that
they could slow it down a little so that they could use the same
crystal to create the clock both for the CPU and the USART. But the
base system had only 16 kB memory, only a little more than half the
size of the 6th Edition kernel. Even without the issue of disks
(which could potentially have been worked around) it really wasn't big
enough for a multiprogramming OS.
=====
Those who remember the earliest UNIX (even if few of us have
used it) might disagree with that. Neither the PDP-7 nor the
PDP-11/20 on which UNIX was born had memory management: a
context switch was a swap. That would have been pretty slow
on floppies, so perhaps it wouldn't have been saleable, but
it was certainly possible.
In fact Heinz Lycklama revived the idea in the V6 era to
create LSX, a UNIX for the early LSI-11 which had no
memory management and a single ca. 300kiB floppy drive.
It had more memory than the 8088 system, though: 20kiW,
i.e. 40kiB. Even so, Lycklama did quite a bit of work to
squeeze the kernel down, reduce the number of processes
and context switches, and so on.
Here's a link to one of his papers on the system:
https://www.computer.org/csdl/proceedings/afips/1977/5085/00/50850237.pdf
I suspect it would have been possible to make a XENIX
that would have worked on that hardware. Whether it
would have worked well enough to sell is another question.
Norman Wilson
Toronto ON
--
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Larry McVoy lm at mcvoy.com http://www.mcvoy.com/lm