Tried some CPU upgrades on a slot-2 HP workstation. Original CPUs were P2 Xeon 450MHz 512KB. As expected, it had no problem with 2x P3 Xeon 550MHz 512KB, and the BIOS correctly identifies them.
The real question was what it would do with "Cascades" core 700MHz 2MB Xeons. It's a little weird.
The 700MHz CPU modules call for 2.8V and have an onboard voltage regulator to produce the voltage(s) that the CPU actually requires. I would assume this was for backward compatibility with older motherboards, and maybe to reduce the current draw. Besides, slot-2 is huge and with the cache now in the CPU and no longer discrete, they had a ton of wasted space in there, and the CPUs were stupid expensive anyway, so I think somebody at Intel just said "What the hell, let's throw a VRM in there."
Anyway, I would have thought these "Cascades" CPUs would work with the existing motherboard VRMs (which are socketed and replaceable). But nope, it only booted after I replaced the corresponding VRM with a Coppermine-era VRM. Not sure why it needs that just to get 2.8V.
I'm still getting a scary red warning light because of the L2 Cache VRM, but I don't think that VRM is actually being used anymore. It boots and runs fine despite the warning light.
The HP BIOS reports the new CPU as a "Pentium Pro 700MHz". Close enough. I benched UT99 real quick and it's almost twice as fast as the Xeon 450MHz.
I can only install one CPU because of the VRM issue. I have more Coppermine VRMs, but the problem is that they're too bulky and the VRM sockets on the motherboard are too close together. I can only install one of them due to fitment. Checked eBay, but I guess people aren't drowning in VRMs anymore because they seem to actually want money for them now. And those that I found are too bulky anyway, just like the ones I already have.
I think I can "shorten" one of the VRMs I have to make it fit, so I'll attempt that.