i am not an expert on that area but frequency has high and low just like bit has on and off. i found this picture that shows how it works.
you can also google it, you will fine some converters and demonstration on how to convert it. so you will see that it works.
my CPUz shows that my RAM are running at 1686mhz. the RAM module here is PC3-12800.
the reason mine is slightly higher then 1600mhz is due to the motherboards bus speed. mine is 140.5.
my BusSpeed to DRAM ratio is 2:12. so if my bus speed are 140.5 i have to divide it with 2 so i get 70.25. now i can multiple it with 12 so i get 843.
and because 843 is my DDR RAM speed i can multiple is with 2, so i get 1686 mhz.
take this for another example. http://3.bp.blogspot.com/-Rk7x5bZcG5...1600/CPU-Z.jpg
he has a BUS speed at 199.9, and a Bus to Dram ratio at 2:6. now divide 199.9 with 2 and multiple it with 6.
you will get 599.7 (or .8 in this example for some reason) with is the Dram Frequency CPUz shows.... and then multiple it with 2 so you get 1199.4 mhz.
i don't understand why your CPUz says FSB : DRAM - CPU