I've got an Abit BH6 1.1 board with a Celeron 466 PPGA chip.

When setting the FSB frequency, I'm able to choose "S" frequencies (like 75, 83, 90, 95, etc) and "N" frequencies (66, 78, 81, 100, etc).

The book says that "S" means that at the frequency "spread spectrum modulation" or something is used and that I should avoid that because it may cause instability under certain conditions.

Can anyone tell me what that means (in English )?

I'd like to use the 90MHz FSB since it uses 1/3 * FSB to get the PCI. Currently, I'm using the 78MHz setting which means my PCI is at 39 MHz and my AGP is at 78.