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From: collinge@uvicctr.UUCP (Doug Collinge)
Newsgroups: comp.sys.atari.st
Subject: Unix on ST (modest proposal)
Message-ID: <213@uvicctr.UUCP>
Date: Thu, 8-Jan-87 00:47:27 EST
Article-I.D.: uvicctr.213
Posted: Thu Jan  8 00:47:27 1987
Date-Received: Fri, 9-Jan-87 21:37:22 EST
References: <8701022135.AA07189@ucbvax.Berkeley.EDU> <7472@utzoo.UUCP> <539@eneevax.UUCP> <10979@sun.uucp>
Reply-To: collinge@uvicctr.UUCP (Doug Collinge)
Organization: University of Victoria, Victoria B.C. Canada
Lines: 34

I am not a Unix guru but I think Henry has made a mistake saying
that fork() can't be done without an MMU.  Here's how:

- parent calls fork()
- copy data space of parent to a swapping buffer or device.
- run parent until she blocks or you get sick of her.
- when you want to run the child exchange the contents of the
  swapping buffer with the data space of the parent.
- usually the child will diddle a bit with its data space then
  exec something else.  When he does we exchange the data once
  more, throw away the swapping buffer, and start up the new
  process in a newly-allocated area. No more swapping.

Of course, the swapping would be pretty tedious for our CPU but we wouldn't
really be doing it very often, only when we start up a new process
most of the time. So, assuming that we only have three or four processes
in our ST I wouldn't expect it to be gross - we have to wait for the disks
to spin anyway.  Besides, isn't it remarkable how good a blitter the 68k
makes? My friend David Harris (C/O me) suggested using the blitter
to do the swapping - nice idea.  I suggest that a little gizmo could be
hooked onto the DMA port that would do the job but it would have to have
a buffer in it I guess, probably too expensive.

Anyway,  I think this could be quite workable on a single user computer
like the ST.  But I probably have overlooked some guru-some fact of Unix
daily life. How about it, Henry?
-- 
		Doug Collinge
		School of Music, University of Victoria,
		PO Box 1700, Victoria, B.C.,
		Canada,  V8W 2Y2  
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