I have been mining for a few days now with different pools and I have had a question niggling at the back of my mind.

If I am solo mining or pool mining and neither of us have a block, what exactly is happening to my CPU's and GPU's to constantly be firing?
Where is all the the effort going?

Is there a way to only run my CPU's and GPU's once a block has been found?

I know it may seem like a simple question to most of you, it's just been really bugging me.