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From: mcdonald@aries.scs.uiuc.edu (Doug McDonald)
Newsgroups: comp.arch
Subject: Re: Let's pretend
Keywords: Intel, 586, windows
Message-ID: <1990Dec19.143749.3216@ux1.cso.uiuc.edu>
Date: 19 Dec 90 14:37:49 GMT
References: <1990Dec18.082623.16648@kithrup.COM> <3058@crdos1.crd.ge.COM> <1990Dec19.052338.3911@kithrup.COM>
Sender: news@ux1.cso.uiuc.edu (News)
Organization: School of Chemical Sciences, Univ. of Illinois at Urbana-Champaign
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In article <1990Dec19.052338.3911@kithrup.COM> sef@kithrup.COM (Sean Eric Fagan) writes:
>In article <3058@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes:
>>  I think we can assume that the 586 will be a superset of the 486. Can
>>someone quantify what would be gained with more registers, say R0-R7?
>
>Yep.  Optimization.  

Yes, in some person's sense. But maybe not speed. IF you add more registers
you have to add instructions to access them. The register addressing 
system, of the 386 is already quite full. Those of you who want more
registers, please explain here on the net exactly what the op-codes you
are going to use to acces those registers. Are you goint to add a byte-
prefix to every register instruction that says "use the special new
register set"? If so, please explain how that would speed execution.
Please remember that any operand that would be put in a register would be in
the cache anyway. 

Only once have I needed more registers than the 80286 already has. Due
to the greater flexibility in use of the registers of the 386 over the
286, I was able to recode for the 386 and get everything in registers.
Result: a 3% speedup.

I think a FAR better idea than squeezing in more registers would be
to take advantage of the fact that the 80x86 was designed from the start
to have an efficient instruction set, leave it that way, and simply use
the chip space to make **everything** faster. 

Doug McDonald