Where do you see 0.79GHz? Usually windows tools (like CPUz) report the instant value, so 0.79GHz could be in idle. Try to make some background work and see again.
you cpu will not always run at its fastest speed to save energy and extend its life, and judging by the speed i would guess its a laptop this also extends the battery life.
would you run you car at max rpm's at a stop light?