luckybob wrote on 2025-05-09, 15:14:

The 5/12 processors have integrated voltage regulators. the 2.8v cpus do not. If a slot-2 motherboard has separate voltage regulators AS YOUR DOES, it means it is designed for the 2.8V processors.

The 2.8V Version with external VRMs can use 5V or 12V VRM moduls? Why different values? Confusing...
And boards from compaq for example dont have external VRM ports.

Yes, the voltage regulator is correct. It can accept 12 or 5v regulators. They output the 2.8v that the chips expect.

Now the 12/5 CPU are directly wired to the power supply and use their internal regulators. That's why you can't mix them.

These regulators are artifacts from the pentium pro era. Where they drew power from the 5v rail and output 2.8v for the cpu.

The pentium 2 xeons used the same regulators. But the switch to 12v as a cpu power source was forged by the p3 xeon. And rather that redesign everything, they just made the new regulators accept 12v input as well as 5v.

And because 99.9% of these xeons were sold to oem, and the intel just decided to integrated the arm on the cpu card to make them happy. You had to be a BALLER to have a dual xeon at home or be ultra special to get one as a workstation. So they didn't care to really offer them to the common rabble.

IT IS POSSIBLE, a 12/5 cpu might not blow up in a 2.8v board. But these parts are just too rare to fuck around with. So I apologize for shouting.

thanks for explanation. I got it now. I agree its to rare to mess up. Than i need to search again for a xeon pair.
I wish intel had design this with a jumper where you switch between external or onboard.

Intel is not a stupid company. (usually)

The 12/5 chips SHOULD NOT blow up if inserted in a 2.8 board. Other way around? most likely. Again, considering the cost of the parts involved and their scarcity, its just not worth it to try, imho. In a properly designed system, an incompatible cpu wont kill anything if inserted into the wrong motherboard. it just wont post. If I was a betting man, I would wager a 75% chance it just does nothing, and a 25% chance of fire.

In THEORY... if you bypassed the onboard regulator, and gave the cpu the desired 5 OR 12v. It should IN THEORY work. I'm also willing to bet there will be other required modifications to make that work and I have zero desire to find out. like pulling certain lines high or low to tell the chip its in a correctly powered socket. i'm going to wager, its like plugging a Tualatin P3 into a Coppermine motherboard.

This build is going to be Awesome if it ever gets built.
Makes me want to take out my Dual CPU motherboards and put one together but I don’t have all the spare components either.

Did some cablework and get Fans installed.

Will the SL3CE work on this board with 12V RMs?