Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mcnc!rti!bcw
From: bcw@rti.UUCP (Bruce Wright)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Was - Re: Xerox sues Apple!!! Now processor wars.
Summary: 80x86 compatibility less than 100%
Message-ID: <3375@rti.UUCP>
Date: 28 Dec 89 18:10:25 GMT
References: <6767@tank.uchicago.edu> <1989Dec17.112127.27333@me.toronto.edu> <899@lzaz.ATT.COM>
Organization: Research Triangle Institute, RTP, NC
Lines: 30

In article <899@lzaz.ATT.COM>, bds@lzaz.ATT.COM (Bruce Szablak) writes:
> 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. Anyone who got on the PC bandwagon in
> the beginning has the satisfaction of being able to use their tried
> and true software on faster and more powerful platforms. The consistancy
> with which each generation of Intel micros maintain compatiblity while
> improving over the previous generation has to instill a certain degree
> of confidence in the future.

The Intel family tends to be upward compatible, but there has certainly
been some software broken over the years going from one processor to
another.  This was especially true back when the 8088/8086 was upgraded
to the 80186 (mostly only seen on the Tandy 2000) and then to the 80286 
(which IBM endorsed with its AT):  many programs which stupidly relied
on timing or processor curios (undocumented instructions which did some
obscure but mildly useful operation) or which relied on some obscure
results (like the contents of the word on the top of the SP when you do 
a PUSH SP) broke when they were run on the newer chips.  Nowadays people
have been sufficiently burned that they usually don't do such things.

There have also been incompatibilities introduced by the BIOS and interrupt
structure on the PC's but that's a different issue.

In general I think this sort of thing tends to be more a question of
intelligent software design (both in the operating system and in the
applications software), not so much a question of different levels
of the chip or the BIOS (though I admit there are exceptions).

						Bruce C. Wright