About the 68010

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                              About the 68010
  Robert Davis              Amateur Radio K0FPC            rdavis@nyx.net
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Every few weeks, a series of exchanges about using the 68010 CPU appears in
the comp.sys.amiga.hardware newsgroup.  A somewhat related discussion
reappears whenever someone asks if putting a higher speed 68000 in an older
Amiga will speed up the computer.

I hope to offer some answers to those questions in this short article.

First, just putting a 68000 rated at a higher speed will do nothing.  The
speed of the CPU is not determined by what is printed on the chip.  The
speed is determined by the computer timing device, its "clock" which is
separate from the CPU.

So putting a 10mhz 68000 in an Amiga means the Amiga won't run any faster
than with an 8mhz 68000.  Think of it like this: Which is faster?  A Yugo
travelling at 55 miles per hour, or a Ferrari travelling at 55 miles per
hour?  Just because you can go faster does not mean you are going faster.

Now there are hacks on Aminet which do change the clock speed of the Amiga
to speed up the CPU while keeping the necessary parts of the computer at
the necessary, slower speed.  Some commercial accelerators have used the
same principle.  AdSpeed and Supra units come to mind.  If you want to
construct one of the hacks, be my guest.  Don't come to me if it does not
work.

Now about the 68010.  That IC does exactly replace the 68000 in its socket
in any older Amiga.  And, that IC does execute some instructions faster
than does the 68000.   Some small loops and all of the more complicated
math instructions are faster on the '010 than on its older sibling.
Therefore the 68010 will run programs which use those particular
instructions faster than the 68000 will run the same programs.   But the
speed up is not very great.  My own tests on an A500 indicate ray tracing
with Imagine isabout five per cent (5%) faster on the '010. 

Many respondents to news postings caution potention users of the 68010 to
get the old program DECIGEL which will fix a problem with one instruction
on the 68000 which is not handled in the same manner on the 68010.  They
tell everyone that some of their software will crash without decigel. 

That is garbage.
   
The particular MOVE instruction which messes up on the 68010 but not on the
68000 will also crash any computer using a 68020, 68030, 68040 or 68060
cpu.  And all programmers have been aware of that instruction and its
problems since the mid-1980s.  More specifically, writers of compilers have
made sure their code generating software did not use that instruction as it
was defined on the 68000.  It has been literally years since any new
software for the Amiga suffered from the MOVE SR,Destination bug in the
68000.

So, the conclusion.  If you want a small speed increase for your older
Amiga (A1000, A500, A2000) changing to a 68010 cpu will do it.  Since the
speed up is small, it will likely be economical only if you get the cpu
chip free or for a very low price, and if you are able to do the
installation yourself, without paying someone else to do the work.

I have 68010 cpus in both my A500 and my A2000.  I paid $5.00 for four of
the '010 cpu ICs at an Amateur Radio swap meet.  For a cost of $1.25 per
cpu, it was worth it for a five per cent speed up.  You must make your own
decision as to whether a 68010 is cost effective for you.

Robert Davis
1107 Mary Apt. 4
Emporia, KS 66801
316 341-9115
rdavis@nyx.net

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