It is my understanding that most CPU's nowadays have integrated GPU's built in. That being said, I know apple relies on the integrated GPU for lower end computers, and for energy reasons as is the case with the 15in rMBP. But what about in the iMacs with discrete graphics cards only? Does the integrated GPU exist and is not used? It seems like a waste to have it there and not use it for anything. Or I could be completely mistaken and if that is the case, I'd like someone to explain where I went wrong. Thanks.