Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!mailrus!tut.cis.ohio-state.edu!rutgers!rochester!pt.cs.cmu.edu!ius3.ius.cs.cmu.edu!ralphw
From: ralphw@ius3.ius.cs.cmu.edu (Ralph Hyre)
Newsgroups: comp.sys.apple
Subject: Re:      Re: Apple II Future
Message-ID: <3954@pt.cs.cmu.edu>
Date: 3 Jan 89 22:03:32 GMT
References: <8812202201.aa08154@SMOKE.BRL.MIL>
Organization: Carnegie-Mellon University, CS/RI
Lines: 34

In article <8812202201.aa08154@SMOKE.BRL.MIL> SEWALL@UCONNVM.BITNET (Murph Sewall) writes:
>...  I haven't heard of a 6502 family chip (in the foreseeable
>future) with a built in memory management capability.  It's possible that
>a IIgs could be made that would blow the Mac away one application at a time
>(might be fine for some users) but the Mac should be able to out multitask
>the IIgs even with the most optimistic of upgrades.
Nope, 95% of the Mac's out there (68000 or 68020-based) don't even have
MMU's, but that's a separate issue from running multiple tasks. A Memory 
Management Unit is useful for protecting tasks from stepping over each other,
but other machines and OSes (Amiga, OS-9, etc, Mac+) seem to multitask quite
nicely without them.

If you run several tasks, then you have to consider the effects of
context switch overhead when switching from one task to another.
Basically this is a fcn of the number of registers in the machine, and
the 65{02,816} have an advantage here (4-5 regs vs 16 or 32 for the 68k).  

65816 also makes it easy to change stack and zero page 'segment' pointers, 
so you can structure things to get a bit more protection than what your 
basic 68k box has. (fewer worries about sanity of that stack pointer
you're about to start using.) 

Meanwhile, I hope all you GS developers are writing position independent
(or at least easily-relocatable) code out there.  This is a case where
the Mac may have had an initial advantage, since code segments must be
relocatable.

Anyway, someday I'll have to write the multitasking OS for the //e
and prove everybody wrong:-)
-- 
					- Ralph W. Hyre, Jr.
Internet: ralphw@{ius{3,2,1}.,}cs.cmu.edu    Phone:(412) CMU-BUGS
Amateur Packet Radio: N3FGW@W2XO, or c/o W3VC, CMU Radio Club, Pittsburgh, PA
"You can do what you want with my computer, but leave me alone!8-)"
--