Subject: Re: NetBSD without MMU
To: None <>
From: Toru Nishimura <>
List: netbsd-ports
Date: 04/14/2002 15:42:46
Ignatios Souvatzis <> wrote;

>> The Zilog Z8000 as well as some either the 8086 or 80286.
> Z8000 has segmenting (and -registers) provided by a companion chip, and I seem
> to recall, paging as well. I've learned Unix on a ZEUS (Zilog Expensive Unix
> System (or maybe "extended"?)).

There were some Z8000 UNIX systems in market at that time. As long as
my personl experience covers, Z8000 system was more suprior (read
crash proof)  to other micro processor based systems (say, 68010 multibus
or VME cage) at the age.

Z8000 had two variations; segmented MMU and paged MMU.  Donno
paged version was actually shipped to market.  Segmentd MMU allowed
any process to have 32 (64?) 64KB protected address ranges which
were quite natural to have separate I+D.  Pointer size is 16 and needs
to "far" designation to access inter-segment pointer reference.  It brought
agonizing pains to port larger applications, say, nroff or vi. I guess the
processor was modeled closely after certain PDP11 designs.

The V7 kernel did "a standard" magic to schedule swapper process in
order to reshuffle/reclaim fragmented physicall memory ranges.

Toru Nishimura