You need IDE, not SATA. I'm not sure if there's a limit on the size or not. Officially, nothing above 128GB is supported, but Apple changed controllers part way through their run, so it depends on which one you've got. It won't hurt anything to use a drive bigger than the 128GB limit, you just won't be able to use more that 128GB of it. Get your drive from Best Buy or some other place with a good return policy and find out.