Now How Is It Done?
All we want is that CPU pin 'B21' is not connected to the motherboard after we plugged in our Slot 1 CPU. A super easy and very efficient way is to simply cover pin 'B21' with a small bit of adhesive tape. To do that, have a close look at the CPU contacts first and check how wide they are, luckily 'B21' is one of the contacts in the lower row. Then cut a small maybe 1 inch long stripe from the tape which is roughly as wide as the contact. It's pretty easy if you've got a Celeron, because it hasn't got a cover, otherwise it's a bit more difficult finding the correct contact. On the Celeron it says 'B1' and 'B121' on its backside, the side where there's no chip on. In case of a Pentium II you need to look at the side which carries the hologram. In both cases it's the side of the CPU which shows the longer row of contacts to the right, the shorter row to the left, both counted from the little notch and seen when holding the CPU the way that the contacts are pointing down. Now find 'B21' by starting to count to the ELEVENTH of the lower contacts starting on the RIGHT side of the CPU. Stick the tape onto this contact and cut off the remaining part of the tape. Make sure that you are using a tape that's sticking very well and check if the tape is fixed properly on the contact so that it won't move when you plug in the CPU. If you have got an automatic motherboard and it ran at 66 MHz so far make sure that you turn down the multiplier. Now plug in the CPU and you will see that like a miracle it's now running at 100 MHz FSB. Voila!
This is how it looks on a Celeron, the Pentium II has the cover over it, but you can still access 'B21' very well without removing the cartridge.
That's what it should look like after using red adhesive tape. You can afford covering a bit of the thinner contacts (B20 and B22) left and right of B21, because the metal clips of Slot 1 only touch the upper part of these two, where the contacts are wide. Be careful that the tape doesn't go up too far, but make sure that it covers all of lower B21.
It's the easiest and most efficient way of getting your Celeron or Pentium II 333 to run at 350 or 400 MHz in *ANY * BX motherboard.