Can FW800 133 MHz board from single 1 GHz machine take a dual processor?

Question

I've read in more than one place that the logic board from the 1 GHz FW800 machine can't be used with ANY dual processor. Can anybody tell me with a reasonable degree of certainty whether this is true or not?
Please don't bother answering based on general principles. I already believe -- tell me if I'm wrong -- that every other MDD FW400 or FW800 board CAN take a dual processor and, except for this question, EVERY processor will work EITHER with EVERY 133 MHz board OR with EVERY 167 MHz board.

Answer 1

From my experience the processor card should be compatible, but don't hang me if I'm wrong.
This page showes how to set different multipliers = bus ratios.
So, according to the default multipliers for the MDDs, you get:
6.5x 133 MHz bus = 864.5 MHz CPU (867 MHz)
6.0x 166 MHz bus = 996 MHz CPU (1.0 GHz)
7.5x 166 MHz bus = 1,245 MHz CPU (1.25 GHz)
Thus, if you put a Dual 1.0 GHz onto a 133 MHz board, you'd get not 1.0 GHz but 800 MHz instead (798 MHz to be exact). The same goes for the 1.25 GHz where you'd get 1.0 GHz (997.5 MHz), and for the 1.42 GHz where it'd be 1,1 GHz (1130 MHz, multiplier 8.5x).
6.0x 133 MHz bus = 798.0 MHz CPU (1.0 GHz → 800 MHz)
7.5x 133 MHz bus = 997.5 MHz CPU (1.25 GHz → 1.0 GHz)
8.5x 133 MHz bus = 1,130 MHz CPU (1.42 GHz → 1.1 GHz)
So, if you alter the bus speed of the board (see here, link is from the xlr8yourmac page linked above) you will be able to use the Dual processors for the 166 MHz bus on your 133 MHz board, then overclocked to 166 MHz, at their designed speeds. If you don't what to change the boards system bus speed the processors will just be underclocked, thus run slower – with all the advantages like less power consumption and less heat emission together with a prolonged lifetime.
To fit the 133 MHz system bus you would have to change the multipliers on the processor daughter card to run at the processors native speeds.
Just one example:
1,000 MHz / 133 MHz = 7.5x
So, if you'd want to run a Dual 1.0 GHz processor on a 133 MHz system board you'd have to alter the multiplier from 6.0x (for the original 166 MHz system bus) to 7.5x (for your 133 MHz system bus) – the resistors to change the multiplier reside on the processor daughter board.
That said, keep in mind that this procedure is *NOT tested or confimed*, but it seems logical, doesn't it?
I had a OWC Mercury Extreme 1.4 GHz processor upgrade placed in a Gigabit Ethernet replaced into a Quicksilver (2001 version). As you can see here, it had set the multiplier to 14x to have it run at 1.4 GHz on the Gigabith Ethernet (100 MHz system bus) and I had to set the jumpers to a multiplier of 10.5x for the Quicksilver (133 MHz system bus).
Thus, if I had put the OWC Mercury Extreme running at 1.4 GHz in the 133 MHz bus Quicksilver unmodified back into the 100 MHz bus Gigabit Ethernet, it would run at 1050 MHz (roughly 1.0 GHz).
That's it. There wouldn't be more to it than that, but the latter source (for changing the motherboards system bus speed) states that Apple put in some protection on the processor daughter card to prevent increase in system bus speed if no dual processor is present. Since this doesn't apply to you as you stick to your 133 MHz system bus it shouldn't bother you.
*But don't blame me* if it should turn out to be completely wrong!
Cheers,
Andreas.