Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!cis.ohio-state.edu!tut.cis.ohio-state.edu!ucbvax!agate!usenet.ins.cwru.edu!ncoast!allbery
From: allbery@NCoast.ORG (Brandon S. Allbery KF8NH)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: 8-bit death
Message-ID: <1991May12.181436.20304@NCoast.ORG>
Date: 12 May 91 18:14:36 GMT
References: <3515.tnews@templar.actrix.gen.nz> <1991May10.183627.29486@neon.Stanford.EDU> <3626.tnews@templar.actrix.gen.nz>
Reply-To: allbery@ncoast.ORG (Brandon S. Allbery KF8NH)
Followup-To: comp.sys.amiga.advocacy
Organization: North Coast Public Access Un*x (ncoast)
Lines: 49

As quoted from <3626.tnews@templar.actrix.gen.nz> by jbickers@templar.actrix.gen.nz (John Bickers):
+---------------
| Quoted from <1991May10.183627.29486@neon.Stanford.EDU> by torrie@cs.stanford.edu (Evan Torrie):
| > jbickers@templar.actrix.gen.nz (John Bickers) writes:
| > My recollection of PDP-11 V7 Unix was that all system calls were invoked 
| > via a trap instruction, with a word afterwords encoding which call was
| 
|     What other considerations are there? I looked up the assembler for
|     the PDP-11, and it appears a TRAP is a bit slower than a JSR. Is
|     there something to do with the state of the machine that is useful
|     to OS functions when a TRAP is used instead of a JSR (for a PDP-11,
|     or for a 680x0?)?
+---------------

TRAP is slower, but JSR doesn't switch the processor to supervisor state.
Yes, Unix runs the kernel in supervisor and user programs in user mode.  Why
do you think Unix programs core dump instead of guru-ing?

+---------------
| > >    Well, the ST thing has desensitized me, otherwise I'd fall over
| > >    backwards laughing at this one. I guess this is well hidden by Mac
| > >    C compilers etc.
| > 
| >   Like I say, isn't this how Unix does it?  
| 
|     If it is, it is also well hidden by the system (as it should be)
|     compilers. MS-DOS's aren't.
+---------------

Actually, 680x0 Unix usually puts the system call in d0.

+---------------
|     In any case, I'm surprised. Is the Amiga OS the only rational one
|     in this bunch, eh?
+---------------

I don't consider running all programs in supervisor mode "rational".  Does/did
the Atari ST do this?  The Mac does, and it shows.

If you're going to multitask, one task shouldn't have the capability of
crashing the whole system.  That's the sort of thing 8088 unixes pull (because
Intel left them no choice).  I expect better of 680x0's....

++Brandon
-- 
Me: Brandon S. Allbery			  Ham: KF8NH on 10m,6m,2m,220,440,1.2
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