Well, first of all, the board uses the 440LX chipset which - unlike the 440BX - does not support FSB speeds > 66 MHz.
To max out the board CPU-wise, you would probably have to go with Celeron CPUs (433 MHz Mendocino core for Slot 1, 733 MHz Coppermine-128 core if you use a slotket, preferably with adjustable VCore).
All Pentium III CPUs are either 100 or 133 MHz FSB, so if you get them to run at all, they won't run at full speed. If running anything newer than Katmai, you might also run into VCore problems because the board might not support other voltages than 2.0V.

Edit: Had a look at the manual, the BIOS seems to support raising (overclocking) the FSB to 75 MHz. Still, not full speed for any of the P3s or other FSB100 CPUs.

It is a known limitation of LX chipset: when installing a Coppermine CPU (doesn't matter whether it is PIII or Celeron) it gives BSOD with both XP and Windows 2000.

gex85 wrote on 2022-01-03, 15:42:

Well, first of all, the board uses the 440LX chipset which - unlike the 440BX - does not support FSB speeds > 66 MHz. To max out […]
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Well, first of all, the board uses the 440LX chipset which - unlike the 440BX - does not support FSB speeds > 66 MHz.
To max out the board CPU-wise, you would probably have to go with Celeron CPUs (433 MHz Mendocino core for Slot 1, 733 MHz Coppermine-128 core if you use a slotket, preferably with adjustable VCore).
All Pentium III CPUs are either 100 or 133 MHz FSB, so if you get them to run at all, they won't run at full speed. If running anything newer than Katmai, you might also run into VCore problems because the board might not support other voltages than 2.0V.

Edit: Had a look at the manual, the BIOS seems to support raising (overclocking) the FSB to 75 MHz. Still, not full speed for any of the P3s or other FSB100 CPUs.

Thank you! You were right, I've tried to install Pentium III E800 since thought it is Slot 1 & saw somewhere that I can try to run it with patched bios. It runs only as 500E Mhz if i set multiplyer to 8, and actually it is detected properly, without any UNKNOWN CPU ID error. Well, Bios works on all of CPU's I've tried so far, WinXP doesn't but - fair enough 😀
Slot 1 CPU are a wild thing to me. I probably should lower my expectations of turning my P2 into P3. I think i have slotket with socket 370, but dunno if it has adjustable Vcore. Well, this time I will be buying CPU for slotket and will try it out. Thanks again!

Paadam wrote on 2022-01-03, 17:23:

It is a known limitation of LX chipset: when installing a Coppermine CPU (doesn't matter whether it is PIII or Celeron) it gives BSOD with both XP and Windows 2000.

Thanks a lot! I didn't knew about that, thought I should try to reinstall OS in such case, but now it makes sense why installation of WinXP via CD even didn't started, but worked with FreeDOS & Acronis Disk Director boot CD without any issues. Maybe some Linux distro will works on it - I've managed to install Q4OS on Mitac-6133 last year, and that one runs really well for laptop with 192 MB of RAM, maybe I should try Puppy Linux or something.