Intel processor: Take the FSB, for example 1333MHz, divide by four as the FSB is quad pumped. 1333MHz/4=333MHz If the clock speed is for example 3.0GHz (3000MHz), divide 3000MHz by 333 = 9. The multiplier is 9 as 333x9=3000MHZ, the FSB x the multiplier = clock speed.
AMD processor (Although this is not technically an FSB speed, just a value used to calculate other frequencies. Clock speed/200=multiplier. For example: 3000MHz/200 = 15
AMD Phenom II X4 955 BE @ 4.0GHz + TU120E lapped - MSI 770-CD45 AM3 - 2x2GB OCZ DDR3 1333MHz - Sapphire HD 4870 - Samsung Spinpoint 500GB 7200RPM 16MB cache HDD - Tagan TG600-BZ Piperock - (Currently open test bed) - Windows Vista Home Premium 64bit.