Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!ucsd!ames!mailrus!cornell!uw-beaver!tektronix!sequent!mntgfx!gssc!bradd
From: bradd@gssc.UUCP (Brad Davis)
Newsgroups: comp.sys.ibm.pc
Subject: Re: replacing a 8086 with V30
Summary: seems to work
Message-ID: <5758@gssc.UUCP>
Date: 2 Sep 88 19:36:02 GMT
References: <162@bach@kulesat.uucp> <9522@cs.tcd.ie>
Reply-To: bradd@gssc.UUCP (Brad Davis)
Organization: Graphic Software Systems, Beaverton Or
Lines: 50

In article <162@bach@kulesat.uucp>, lily@kulesat.uucp writes:
> 
> Does anyone out there have any experience in replacing an Intel
> 8086 processor by another in a PC-clone (Schneider in my case).
>

   I've had a V30 in my AT&T 6300 for a year or two (time flies...) and
never had any problems.  I just added an 8087 and it appears to work,
though I haven't used it much yet.

In article <9522@cs.tcd.ie> omahony@cs.tcd.ie (Donal O'Mahony) writes:
>
>I too am considering using a V30 in an Amstrad PC.  The ads in BYTE for
>V20/V30 claim a 10-40% speedup.  I presume that these processors
>execute some instructions faster than their Intel counterparts.
>Can some knowledgeable person say what the instructions are ?
>
   The V30 understands the 8086 opcodes, the 80186 extensions, and a couple
of Vx0-specific instructions.  It is measurably (probably 10%) faster than
the 8086 overall, but there are a few areas where the NEC chips are
very much faster, and it was no doubt these that gave rise to the 40%
figure and to some of the massively distorted Norton benchmark numbers.

   I don't know precisely what these instructions are, but I'll give you
good odds that DIV, IDIV, MUL and IMUL are among them.  That and effective
address calculation delays seem to be the worst problems of the 808x, and
hence where NEC could make the biggest improvements.

   You can set a bit in a register somewhere and the V30 will emulate an
8080 instead (I haven't used this but I hope to some day).  I believe that
this is probably what hangs some programs: if you muck with flag bits
that Intel marked as reserved, you might find yourself in 8080 mode.
And since the 8080 isn't compatible with the 8086, you are dead.

   And of course you will throw off delay-loop oriented software because
you are faster than the XT you appear to be.  But with an 8086 you are
in that boat already thanks to the faster 16-bit bus.

   Verdict: makes games tougher, but if you really want to speed up your
system, it is ABSOLUTELY THE BEST PERFORMANCE BUY IN EXISTANCE.

   Brad Davis

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