"but in the Bios settings it shows that it is in fact 24 x 100 MHz not 12 x 200"
"We should say its 6x400, which is reality. Here's why we do it differently.
In your first example where the front side bus was 100mhz and the multiplier was 4, that front side bus operated off of a 100mhz clock. Think of the clock as a 12hour clock with a second hand spinning around 100 million times a second. In that era, the front side bus would transmit bits every time the clock struck 12, or 100 million times a second.
In this era of a 2400mhz p4 (which has a quad pumped bus), the system clock is still 100mhz just like before, but now bits are transmitted when the clock strikes 12, 3, 6, and 9 (that's the quad-pumped part), resulting in 400 million transmissions per second. So this is called a 24x100 cpu, but really should be called a 6x400 cpu. The reason it isn't is because the convention does not follow throughput, but the actual construction of the cpu speed, which indeed is dividing the system clock (100mhz) by 24. "
Maybe that will help you understand a little better