Xref: utzoo comp.sys.mac:13955 comp.windows.misc:291 comp.sys.m68k:816
Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!pasteur!agate!eris!mwm
From: mwm@eris (Mike (My watch has windows) Meyer)
Newsgroups: comp.sys.mac,comp.windows.misc,comp.sys.m68k
Subject: Re: A/UX window systems, Mac toolbox, etc
Message-ID: <7681@agate.BERKELEY.EDU>
Date: 15 Mar 88 06:25:25 GMT
References: <4129@hoptoad.uucp> <283@rhesus.primate.wisc.edu> <1710@ssc-vax.UUCP> <9829@steinmetz.steinmetz.UUCP> <7593@apple.Apple.Com> <3609@bloom-beacon.MIT.EDU> <7656@apple.Apple.Com> <7670@apple.Apple.Com>
Sender: usenet@agate.BERKELEY.EDU
Reply-To: mwm@eris.UUCP (Mike (My watch has windows) Meyer)
Followup-To: comp.sys.68k
Organization: Missionaria Phonibalonica
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[Followups have been pointed to comp.sys.68k.]

In article <7670@apple.Apple.Com> goldman@apple.UUCP (Phil Goldman) writes:
<I think one point you are both missing out on is that preemptive multitasking
<requires hardware support not available on a 68000.

Right. So how did Sun, Apollo, Amiga, Sage, Stride and a multitude of
others manage to market 68000 systems that did preemptive
multitasking?

All you need to manage preemptive multitasking is a way to take
interrupts that allows you to save the old context, and the mechanisms
needed for a non-preemptive scheduler.

Being able to save the old context can be a bear - you have to either
not interrupt instructions, or be able to rewind/restart an
instruction. On the 68K, about the only thing that causes serious
problems is bus & address errors. Address errors are sufficient to
abort the processes causing it (or panic the OS). Bus errors do the
same in non-VM systems. In vm systems, they could indicate a page
fault, which has to be dealt with.

Here is where the 68000 has problems: there's not enough information
around to restart a process that page faults in the middle of some
instructions. The 68010 & later processors fixed this. But people
found ways around that problem with thoe 68000.

<-Phil Goldman
<Apple Computer

	<mike
--
Il brilgue: les toves lubricilleux			Mike Meyer
Se gyrent en vrillant dans le guave,			mwm@berkeley.edu
Enmimes sont les gougebosqueux,				ucbvax!mwm
Et le momerade horsgrave.				mwm@ucbjade.BITNET