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From: mark@mips.COM (Mark G. Johnson)
Newsgroups: comp.sys.m68k,comp.arch
Subject: Moto's data predicts 68040 performance well below 20 MIPS
Message-ID: <40088@mips.mips.COM>
Date: 12 Jul 90 16:05:15 GMT
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The June 1990 issue of _IEEE_Micro_ contains an article about the
Morotola 68040, written by some of its designers.  The article agrees
with some of the advertising copy, saying "The sustained
performance level is 20 VAX-equivalent MIPS and 3 Mflops at a clock
speed of 25 MHz."  (1st paragraph, 4th sentence).

Later in the article, Figure 2 is particularly interesting; its caption reads
   "Processor performance relative to the 68020   versus   cache size
    (where the 68020 equals 1)."

For the cache sizes actually used in the 68040 (4Kbytes), the
performance plotted in Figure 2 [68040 normalized to 68020] is in
the range 3.6X to 4.3X, depending upon the workload.  Most of the
benchmarks shown are at 4.1X.

So, the data and the claim that 68040==20VAXmips  implies that the earlier
68020 has a "sustained performance level of 4.9 VAX-equivalent MIPS"
(4.9 = 20/4.1).  Does anybody seriously believe this?

About the most impartial data I could find was for the Hewlett Packard
HP9000 model 370 machine.  This uses a 68030 (not 68020) at 33 MHz (not
25 MHz) and achieves a geometric mean of 3.9 SPECmarks [ref. SPEC
newsletter v1#1].  It seems reasonable to suspect the 68020 is no
better than the 030 in performance {else who'd want the 030?}, so we
conclude that the 020's performance is, at most, 3.9 VAX-equivalent
MIPS.  This makes the 68040 a 16 VAXmips machine (at most), not 20 VAXmips
as advertised.

Of course the best method would be to lay hands on an actual computer
system that uses the 68040 and benchmark it; presumably Motorola
and/or NeXT and/or HP will do this someday.  Prediction: the SPECmark
will be significantly below 20.0.

Disclaimer: I'm biased.  Check out the SPEC newsletter and the issue
                         of IEEE Micro to see if I've distorted the
                         facts.  (I assert that I haven't)
-- 
 -- Mark Johnson	
 	MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086
	(408) 524-8308    mark@mips.com  {or ...!decwrl!mips!mark}