UNDERclocking GPU

I'm pretty sure underclocking won't save you any battery life. The current theory on how to maximize battery life is that the faster a processor gets the job done, the sooner it can return to a state of deep sleep. If your gpu is not being used, great, it will sleep. If it is being used, then the sooner it gets done the sooner it can return to sleep. That's why tests show that a higher clock speed processor actually lengthens battery life, rather than shortening it.

At least that's my understanding.

 

IF you can drop the voltage to the GPU after underclocking it, that will save you some power and heat, but the difference probably won't be worth it. Just like CPUs, every GPU has a different voltage requirement depending on how "good" the chip was fabricated. If you drop the voltage too much you're going to have stability issues.

Also, OS X does make pretty good use of the GPU, so DocSmitty is correct; letting it get the job done and go into an idle state more quickly might negate any benefit of underclocking.

 

Even if underclocking your gpu would save battery (which is questionable), the amount would be pretty dang small and it would make your system less stable. You can try aticellerator if you like and see if it works on your system, but I'd really suggest against it.

http://thomas.perrier.name/index.html

 

I thought I read somewhere that Apple already underclocks the 8600M's in the 15" MBP's?

 

Be aware that changing the clock speeds of your CPU/GPU voids your warranty with Apple when it comes to notebooks.