Path: utzoo!attcan!uunet!mcsun!hp4nl!eutrc3!tuewsd!wsinrn
From: wsinrn@lso.win.tue.nl (Rob J. Nauta)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Was - Re: Xerox sues Apple!!! Now processor wars.
Message-ID: <816@tuewsd.lso.win.tue.nl>
Date: 13 Jan 90 11:27:50 GMT
References: <899@lzaz.ATT.COM> <1360@unocss..unl.edu> <1990Jan1.202916.13637@polyslo.CalPoly.EDU>
Organization: Eindhoven University of Technology, The Netherlands
Lines: 37

In article <1990Jan1.202916.13637@polyslo.CalPoly.EDU> tdrinkar@cosmos.acs.calpoly.edu.UUCP (Terrell Drinkard) writes:
>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.
  
>> 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).


Hmm, consider a BYTE column by Jerry pournelle where he described that his
copy of the Amiga game Populous wouldn't work on his A2500, the solution
was to boot with the left mouse depressed which forces the A2500 to boot with
the 68000 instead of ther default 68020. Makes you wonder why Commodore
plugged in an extra 68000... There is an undocumented instruction in the
68000 which isn't supported in later models, but which gets used extensively
by machine language programmers because it's so convenient... Luckily
compilers are smart enough not to generate this one...


flame away, I'm ready ! :-))
Rob J. Nauta