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From: tdrinkar@cosmos.acs.calpoly.edu (Terrell Drinkard)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Was - Re: Xerox sues Apple!!! Now processor wars.
Message-ID: <1990Jan1.202916.13637@polyslo.CalPoly.EDU>
Date: 1 Jan 90 20:29:16 GMT
References: <899@lzaz.ATT.COM> <1360@unocss..unl.edu>
Sender: news@polyslo.CalPoly.EDU (News Guru)
Reply-To: tdrinkar@cosmos.acs.calpoly.edu.UUCP (Terrell Drinkard)
Organization: Cal Poly State University -- San Luis Obispo
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In article <1360@unocss..unl.edu> ho@fergvax.unl.edu writes:
>From article <899@lzaz.ATT.COM>, by bds@lzaz.ATT.COM (Bruce Szablak):
>> More importantly, will my 68000 software run on a 68020, 68030, 68040
>> etc?  Sometimes yes, sometimes no... The real significance of the 
>> Intel chips are that they are upwardly compatible.
>
The reason older Macs cannot run some of the newer Macintosh
software is NOT that the new processor have different instruction
sets, it is because of upgrades in the ROMs.  The same thing
happens with the PCs.  Remember the original PC?  Could you run EGA
graphics on it?  Could you even run a hard-drive on it?  No.  But,
with appropriate upgrades in the BIOS, it is now possible to run
all this stuff and more.  The same thing happens to the Macintosh;
new features become available and are used by various applications.
And since these features are not supported in the older ROMs (the
Mac's BIOS if you will) the older Macs can't run those
applications.

>THIS IS NOT A FLAME.  Ah, now that the disclaimer's out of the way...
>
>Is this because of the processor chip itself, or an incompatible
>platform?  Are there actually 68000 instructions that don't work the 
>same on an 030, or is it just that the Mac {SE, II, SE/30} has a 
>different structure which is (usually) shielded from ("polite") 
>applications throught the System software?
>
>I don't know.  I'm just asking.  It does seem odd to create an 
>incompatible chip.  Makes me wonder what the marketing department at 
>Motorola is up to.

In a slightly different vein:  the instruction sets for the 68010,
68020, 68030, and even the 68040 all contain the instruction set of
the 68000 as a subset.  Each revision of the processor *added* more
features.  The only variation on this that I'm aware of is with the
68030's MMU command set differs with the 68020 + 68851 (PMMU)
instruction set by one or two commands (depending on which
direction you are looking from).

>	... Michael Ho, University of Nebraska
>Internet: ho@hoss.unl.edu		USnail:  115 Nebraska Union
>BITnet:   cosx001@UNLCDC3			 Lincoln, NE 68588-0461

I would also point out a much more complete answer to the questions
about how to do xxx on the Mac in an earlier message.  I'd
reproduce it here, but it's New Years Day, and I'm wanted back in
bed soon.  :-)
 
Terry

Disclaimer et la Signaturo:
Hell no, I'm not responsible for what I say!  If everyone were
responsible for what they said, we'd have had a balanced budget in
1984.