Overclocking both the 7800 GT and GTX is a little bit more complicated than usual. This is because there are three different clock speeds to deal with - the vertex, shader and ROP clocks and these are all controlled by the root clock. The root clock is the one you will be tweaking in overclocking tools such as ATI Tool or Riva Tuner. When you adjust the root clock, you actually adjust these three clocks.