Yes, I'm making a thread that is solved even before I post it, but I thought it might be useful to other and future Vogoners.

I have a Intel VS440FX motherboard paired with a PPro 200MHz (256k cache). I have Windows NT 4 installed on it. Out of the blue, it started exhibiting serious performance issues... like, crawling. Minutes for Windows Explorer to load after logging in. Easily 5 times as long to unzip the same zip file as on my 486 33MHz. Copying files over network (Intel e100 NIC) at <50kbps. Everything is obviously very CPU bound. Rebooting and multiple power cycles made no difference.

I scratched my head for a long time trying to figure out what was wrong... why was this PPro performing so much worse than my 486 33MHz? Was there something wrong with the CPU? The motherboard? Did my Hard Disk die, maybe? Had I somehow unknowingly disabled the CPU cache?

Well, on the hunch of the last one there, I looked all through the BIOS settings, but I could not find anything about controlling the enable state of the CPU cache. So, in an act of desperation, I pulled the CMOS battery and let the CMOS clear.

Well, unfortunately I have no real hard evidence to say what my problem really was, and to provide an anticlimactic ending, clearing the CMOS fixed it. I can only assume it was something like CPU cache being disabled. Back to speedy number crunching goodness now! Hopefully this helps someone. Oh, also, another PSA, put a new battery in... I've learned that Intel VS440FX really does not like a low CMOS battery and does weird things including not booting.