Vždyť tam jsou příklady. Nastavuje se to v BIOSu.

The CPU External Frequency for Athlon XP is half of the FSB Frequency. Thus, with a 333MHz FSB, the CPU External Frequency is 166MHz.
On the ASUS A7V8X-X Motherboard, for a 333MHz FSB Athlon XP, the setting for CPU External Frequency (MHz) should be 166/33. 33MHz is for the PCI Bus, while 166MHz is for the System Bus (a.k.a. External Bus).
For PC2700 RAM, the Memory Frequency is 333MHz.