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From: gnu@sun.uucp (John Gilmore)
Newsgroups: net.micro,net.micro.68k,net.arch
Subject: Re: 68020 vs. 32032, pros and cons
Message-ID: <1254@sun.uucp>
Date: Tue, 12-Jun-84 04:00:28 EDT
Article-I.D.: sun.1254
Posted: Tue Jun 12 04:00:28 1984
Date-Received: Thu, 14-Jun-84 06:37:07 EDT
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Organization: Sun Microsystems, Inc.
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> National seems to have decided to do simpler components optimized to what they
> consider to be the average use, rather than fancy parts that can be adjusted
> to optimize your particular use.  In exchange, national was able to produce
> their parts, while motorola is still dreaming.
Motorola's first parts were simple too, but they've been improving them
over the years.  (Over half of the 68000 microcode was rewritten for the
68010.  Probably all of it is being done again for the 68020.)

Nobody can dispute that the 16032's instruction set is seriously
orthogonal, while the 68000 series only makes a half-hearted attempt.
Nick Tredennick, who wrote the 68000 microcode, claims it's mostly his
fault, because he couldn't make it all fit on the chip.

The big Motorola win for me is performance.  Motorola has shown that
they can produce full-speed chips; we had a 16MHz 68000 sample close to
two years ago, and many people run 12.5MHz production.  People from
National keep telling me that the 10MHz part is real, but somehow their
customers keep mentioning 6MHz.  Does a 6MHz 32032 outrun a 12.5MHz 68000?

Also, I got the impression that the 32032 is not even close to twice as
fast as the 16032 -- my correspondent seemed to think it ran roughly
the same speed, since they didn't increase the internal processing
speed even though they doubled the memory bandwidth.  (68000-era
processors and bus interfaces run at almost exactly the same speed, which
means that just widening the bus would not speed them up much.)  Motorola
is speeding up the processor clock rate, the internal algorithms, the
bus width, and the bus cycle time in clocks, while reducing the demand
for bus accesses -- all by significant factors.  I'll be glad to hear
differently if National really did improve the guts of the 16032 to
make the 32032 -- can anyone confirm or deny?

> You will pay for that extra bit of performance through the nose though.
OK, tell me the cost, don't just wave your hands.

PS:  If you want to build a co-processor of your own, don't try to hang
it on a 32032; the CPU decodes the co-processor instructions, so you'll
need a new CPU chip too, unless your co-processor instructions look a
lot (well, OK, exactly) like their float box's.  Motorola got it right.

PPS:  I'm pleased to see that unlike Intel, National is aggressively
encouraging people to hook up their float chip to 68000 systems.  Digital
Acoustics is having great fun with them; they claim a 12.5MHz 68000 can
keep two 16081's busy at once for serious numeric work.