[andrewas]

One of the important things about CPUs and GPUs is that they themselves dont know how fast they're supposed to run. They take a clock signal from the board their mounted on, and run at that speed.

Also, since boards are designed to support multiple chips, they have to have clock generators that can run at multiple speeds. On a CPU, you can set the clock speed and some other associated settings at will, and run a 1Ghz chip at 2Ghz. Or you could, if you could keep it cool, because the faster it goes the hotter it runs. Run it above its intended temperature and you half the lifetime of the chip for each 10 degrees you add.

On graphics boards, the GPU is installed at the factory, so there's no need to allow the clock to be altered by the end user. Which is why you need to mess around in the registry to do it. The benefits and risks are the same. Extra power = extra heat.