Aha, so it does come with a ROM card... Interesting. Perhaps it patches the Apple ROMs or replaces them so that the overclocking will work stably?

Thanks for detailing this complicated overclocking scheme!

Click to expand...

Did that overclocking kit let you adjust the clock speed with software?

If so, my guess is that the card in the ROM slot is not a ROM, but is using the ROM slot for access to the address and data busses.

You tell the software what speed you want. The software writes a speed code to an unused location in the Mac's address space. The message shows up on the ROM slot (as well as the rest of the address/data bus) and the card in the ROM slot decodes the message and passes it to the overclocking hardware, thus setting the speed.