🚀 go-pugleaf

[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
--
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