Question about CPU clock multipliers?

I've been reading about CPU clock multipliers and I'm really confused. If a CPUs advertised clock speed was 3.0ghz but you had a really slow front side bus would it make it less than 3.0ghz? Is 3.0ghz just the approximate speed? In other words, does your FSB speed affect the advertised CPU clock speed I read that CPU speed=CPU multiplier x FSB speed. If it does just depend on your FSB, then how do they determine the advertised speed? Is the multiplier determined when you install the CPU, or is the multiplier already set in the CPU. Thanks in advance. :D Sorry for such a long question.