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From: peter@sugar.UUCP (Peter da Silva)
Newsgroups: comp.arch,comp.unix.wizards,comp.os.misc
Subject: Re: "fork" with no MMU (was Re: Shared libraries (Was: ...)
Message-ID: <895@sugar.UUCP>
Date: Thu, 22-Oct-87 13:41:27 EST
Article-I.D.: sugar.895
Posted: Thu Oct 22 13:41:27 1987
Date-Received: Sun, 25-Oct-87 08:39:42 EST
References: <8714@utzoo.UUCP> <286@usl> <73@usl-pc.UUCP> <881@sugar.UUCP> <31162@sun.uucp>
Organization: Sugar Land UNIX - Houston, TX
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Xref: mnetor comp.arch:2695 comp.unix.wizards:5053 comp.os.misc:312

In article <31162@sun.uucp>, guy%gorodish@Sun.COM (Guy Harris) writes:
> > So tell me... how did they implement fork() without an MMU? Did they do
> > addres fixups on running code, or did they require all code be relocatable
> > (not an unreasonable request on the PDP-11, by the way, and one place where
> > the 11 has the 68000 beat hollow).
> 
> Neither.  They only kept one process in memory at a time, using swapping to do
> context switches.

That still doesn't disprove my claim that UNIX won't run on a system with
512K, two floppies, and no MMU. I don't consider swapping to floppies as
an acceptable method of context switching. Maybe totally hacked 8" drives
would do, but I'd want at least a hard disk.

(Yeh, I know MINIX does in-memory copies for the same purpose. That'd be
barely acceptable. It's not going to hum along as well as OS/9 or AmigaDOS,
though. And UNIX executables tend to be quite a bit larger than Minix' 10K.
Moving 10K of data for a context switch is bad enough. Imagine doing that
with csh(1).)
-- 
-- Peter da Silva  `-_-'  ...!hoptoad!academ!uhnix1!sugar!peter
-- Disclaimer: These U aren't mere opinions... these are *values*.