A P2-400 is a 100MHz FSB CPU with fixed multiplier, so you won't be able to run it at stock speed on an i440LX board in any event, as the LX only support 66MHz FSB, and 4x66=266MHz. Some LX boards wil run stable up to 83MHz, but that still means max 333MHz.

Given the multiplier is locked at 4x regardless, there are only two possible explanations for why you're seeing 200MHz:
- either the FSB is set at 50MHz, in which case 4x50MHz=200MHz. Set it at 66MHz and it should correctly switch to 266MHz.
- or the CPU is actually running at 266MHz, but as the BIOS doesn't know the CPU, it's giving incorrect information.

If you know FSB is set to 66MHz, run some tools (which are available depends on your OS, which you don't mention) to detect CPU speed directly.

dionb wrote:

Given the multiplier is locked at 4x regardless

Note that the earliest Pentium II 400 specimens were not multiplier locked.

In that case it could be running at 3x 66MHz indeed.

OP, if you suspect that might be the case, please be more specific than:

switching the jumpers on the board does not seem to make a difference.

Exactly which settings did you try with which jumpers?

I set the FSB to a 100 MHz mode that is certainly not standard for this chipset and a 4x multiplier.

I fixed my problem, switching to 66 MHz FSB allows me to change the clock speed

As the image shows this Pentium II 400 is from week 2 1999: surely locked to 4x.

It does appear to be that way. 100 MHz FSB causes complete system instability, so I guess I'm stuck at 266 MHz 😢

TheMLGladiator wrote:

It does appear to be that way. 100 MHz FSB causes complete system instability, so I guess I'm stuck at 266 MHz 😢

Using an EX chipset, which is 66 MHz, it's impressive that the board event has 75, 83 and 100 MHz settings on the clockgenerator ..