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From: jbuck@galileo.berkeley.edu (Joe Buck)
Newsgroups: comp.arch
Subject: Re: Let's pretend
Keywords: Intel, 586, windows
Message-ID: <9876@pasteur.Berkeley.EDU>
Date: 18 Dec 90 23:20:44 GMT
References: <3042@crdos1.crd.ge.COM> <1990Dec18.082623.16648@kithrup.COM> <15145@ogicse.ogi.edu> <24117@grebyn.com>
Sender: news@pasteur.Berkeley.EDU
Reply-To: jbuck@galileo.berkeley.edu (Joe Buck)
Lines: 25

In article <24117@grebyn.com>, ckp@grebyn.com (Checkpoint Technologies) writes:
|> Just think of it.  Intel releases the 586, and to improve performance
|> they remove a few complex instructions and replace them with one or two
|> simpler but faster instructions.  No software that used those
|> instructions will run.  Intel earns a bad rep and sells zero chips as
|> the journalists take Intel apart for producing an incompatible chip.

No, I'm afraid not.  What you do is you get an illegal instruction trap
when the wierd instruction is run, and the trap handler then emulates
the instruction.  The chip-maker releases the code for the trap-handler
(makes it public) and the PC-clone folks put it in their BIOS ROMs and
the Unix-port people put it in their kernels.  The lowly user has no idea
that anything is different, since the 586 is so much faster that the
emulated instruction is faster than the original.

No doubt some ignorant journalist will write an article making the point
you make.  Everyone in the know will proceed to laugh at that journalist.

It's been done before, of course; MicroVAXes do just this (they don't
support the fancy VAX instructions but emulate them with traps).


--
Joe Buck
jbuck@galileo.berkeley.edu	 {uunet,ucbvax}!galileo.berkeley.edu!jbuck