cpu multipliyer and Host clock

[Atreyo Bhattacharjee]

Why do we need a host clock, and a cpu multiplyer when OC? Why cant it all just be one clockspeed that we increase or decrease?

 

[CountMike]

Because they OC different things, different ways. While multiplier OCs only processor, FS/BCLK also OCs other parts like chipset, PCIe, RAM etc. You are free to use only one of those methods but some BIOS also have settings for performance that intelligently adjust both values for best stability and performance.
My favorite way of OCing is to use multiplier to find CPU and it's voltage maximums, lower it by one step and use FSB/BCLK to fine tune performance of other parts.