it's DDR for "Double Data Rate" so your RAM is actually 1333/2=667 MHz
Your FSB (if your CPU still has one of these it's already quite old...) will probably be something like 100 MHz, 133 MHz, 166 MHz, or 200 MHz.
This FSB is multiplied by the multiplier, resulting in your CPU Clock speed
ex: AMD XP 2000+
FSB: 133 MHz
Clock speed = 133x12.5 ~ 1.67 GHz
RAM clock needs to be matched to the FSB speed, for old DDR RAM, they had DDR266, 333 and 400 which was divided by 2 for FSB speed.
The modern Intel CPUs only use a "bus" now, and I'm pretty sure they arent locked to RAM speeds any longer as they were in the past.
You can only really overclock "K" series CPUs by increasing the multiplier and voltages these days, the BUS is not very flexible.
Past: Buy faster RAM, increase FSB
Now: Buy whatever RAM, buy K series Intel or AMD Black CPU, over-multiplier like crazy
To get 4.0 GHz, u would for example, do
BUS: 100 MHz
Clock speed = 100x40=4000MHz
first post was from 2004 - This article needs to be like.. locked please? lol