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From: rehrauer@apollo.HP.COM (Steve Rehrauer)
Newsgroups: comp.sys.amiga
Subject: Re: 68020 and 68030 ?
Keywords: 020, 030
Message-ID: <4d6635ba.20b6d@apollo.HP.COM>
Date: 14 Oct 90 21:06:00 GMT
References: <211@nos850.UUCP> <4186@bingvaxu.cc.binghamton.edu>
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Reply-To: rehrauer@apollo.HP.COM (Steve Rehrauer)
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Organization: Hewlett-Packard Apollo Division - Chelmsford, MA
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In article <4186@bingvaxu.cc.binghamton.edu> podop03@bingsuns.cc.binghamton.edu (Kriston J. Rehberg) writes:
>  Be sure when you buy the card that it
>comes with a math coprocessor, because having an accelerator card
>without one is not too good of a thing to do (math coprocessors take
>over integer functions so the 680x0 can do other things!).

   Goodness, no!  The Motorola math coprocessors do floating-point,
and int<->float conversions, only.  Chip->chip communications between
a 680x0 and a 6888x coprocessor are slllooowwwww by comparison with
integer instructions that the 680x0 executes itself.

>  By the way,
>a 68040 is a processor that contains the CPU, MMU and the math
>coprocessor!  By putting all of this stuff together you get the
>opportunity for a good speed increase.

   Given equal clock rates, anticipate 1-3x integer performance and
2-10x floating-point performance going from a 68030+6888x to a 68040.
The integer speedup is mostly due to bigger instruction & data caches.

   (The 68040 doesn't implement the full instruction set of a 6888x
FPU, so your float mileage will vary depending upon the instruction
mix in your code.  If you take code that was compiled for a 6888x
coprocessor and run it on an '040 box, you're probably going to be
trap-emulating some 6888x instructions, which is a big performance
loser.  I think some people are going to be surprised when they take
big number-crunchers compiled for a 68030+6888x and move it onto a
68040 -- it mayn't run all that hot, as it would if the compiler were
tuned for the 68040 float instruction mix.)
--
"I feel lightheaded, Sam.  I think my      | (Steve) rehrauer@apollo.hp.com
 brain is out of air.  But it's kind of    | The Apollo Systems Division of
 a neat feeling..." -- Freelance Police    |       Hewlett-Packard