From: mks@cbmvax.commodore.com (Michael Sinz)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: GForce 40MHz OVERCLOCKING........
Date: 2 Oct 92 13:07:13 GMT
Reply-To: mks@cbmvax.commodore.com (Michael Sinz)
Organization: Commodore, West Chester, PA

cpw8034@venus.tamu.edu (ALAN CHIPIN WEN (409)693-2924) writes:
>>Simple...  A 40MHz chip's *MAX* clock rate is 40MHz.  Some parts may happen
>>to run a bit faster, but if they all ran faster, Motorola would sell them
>>as, say 46MHz parts rather than 40MHz.  (People pay more for high speed
>>parts)
>
>Wrong.  CPU's are labeled and sold to what the manufactorer believes is
>a stable clockspeed.  Just about ALL CPU's can oscillate a bit faster than
>the rate printed... it's just that when pushed beyond the limit can cause
>mechanical problems due to heat dissappation (sp?).  You can push a 40Mhz
>to about 45Mhz if you can find the right oscillation crystal and a proper
>method of providing heat sinks.

I won't get into this war.  Just let it be noted that:

1)  If Motorola could call them 45MHz then they would as marketing always
    wants faster parts.

2)  The internal designs of these chips are many times very tightly tied
    to the clock rate.  For example, the 68040 design is different for
    the 33MHz part than the 25MHz.  In fact, they use two different chip
    fabrication processes.

3)  Going beyond the specification may work on one chip for most of the
    instructions some of the time (or most of the time) as long as nothing
    runs right at the spec limits at the new clock and you don't do....
    In otherwords:  It does not work.  A number of times I have taken
    my processor test software to a board that was over-clocked and found
    one or more instructions that caused incorrect results.  In fact,
    in one case, it was only a certain instruction sequence that caused
    a data reguster to have the wrong value.  Now, how can you feel safe
    with your data in a machine like that?  Would you want the airplane
    you are flying in to be run by an overclocked chip?  How about your
    bank statement being calculated by one?  Or your hard drive controller
    software running on one?  Think about that...

4)  If you ask competent engineers about running such complex parts beyond
    the designed specification, they will say "Don't do it" and if you
    say you need the speed, they will say "Get a faster part"   There
    is a reason why a number is stamped on a part.

>You can find example in MMR's ads.  Some 030's are rated higher than the
>actual chips... like 26Mhz's, 38Mhz's, and such.

Just because some companies are running the CPU faster than the rating
does not mean it is a valid operation.  In fact, the current engineer at
CSA (he did not do the MMR but he did do the 040 board and all the new
ones) is very against overclocking.  He also has seen the problems of
going beyond spec and will not put his name on anything that does.

Official Commodore statement is that if an Amiga as problems (hardware
or software) and an over-clock CPU is being used, it is up to the vendor
of the over-clocked CPU to solve the problem.  Period.

/----------------------------------------------------------------------\
|      /// Michael Sinz  -  Senior Amiga Systems Engineer              |
|     ///                   Operating System Development Group         |
|    ///   BIX:  msinz      UUNET:  mks@cbmvax.commodore.com           |
|\\\///                                                                |
| \XX/     "I think not." said Ren'e Descartes, then he vanished.      |
\----------------------------------------------------------------------/