How to overclock a SonnetTech NuBus G3 card

I got some mails from people who don't know how to compile, or lack a compiler program. I don't really have time to make an extension for every NuBus machine (I don't even own a NuBus mac anymore), or to teach C/C++ compilers to everyone. Since the overclocking method is unconventional, makes very little advantage in processor speed, and was only for experimenting/checking how the card works, I suggest that you forget about this if you don't know how to build the little extension to your needs.

I was able to overclock the processor card by writing an extension
that faked the 6100, 7100 or 8100's busspeed before the G3 card loaded. This way, the card chose a higher multiplier to compensate, resulting in a higher processor speed. No hardware tweaks/soldering involved. :)

Here's the results, performed on a 8100/80 with a SonnetTech Crescendo 220.

Faked busspeed	Faked procspeed	Result procspeed	RC5 keyrate	Processor temperature
30	60	<crash>	-	-
31.5	63	280 MHz	859	44° C
33	66	260 MHz	810	43° C
36.5	73	240 MHz	745	39° C
40	80	220 MHz	693	35° C

I used the same method on a 6100/66 with the same card, which worked also, only with other busspeeds/procspeeds.

Note that every other PowerMac model has its own busspeed variations, so if you have a 7100 or 6100/60 or something, it'll be a matter of trying out the nearest lower busspeed.

Also note that the overclocking renders the card pretty unstable. 280 MHz is fun to try out for a few minutes, but will crash your Mac every other minute.

Gonna try ? You'll need this.
This is the source for the extension that fakes the busspeed/procspeed + a compiled extension built for the above configuration. It was compressed as a StuffIt 5 archive, so you'll need Expander 5 to unpack it.

To make it work, modify the source to your Mac's configuration, compile the extension, and make sure it loads before the Crescendo extension does. You can do this by changing the extension's filetype to "scri" and adding one or two spaces to the beginning of the title.

Please try and do this yourself. I can't compile a copy for everyone who sends me an email. I don't even have a compiler program at hand. If you do, but don't know how to compile, I'm sure a manual came with your software package.

Disclaimer: This page is provided for educational purposes. If you chooseto try this out on your machine, it will be on your own risk and responsibility, not mine.

Robert Sixkiller, sixkiller@ukonline.co.uk