I'll be purchasing my first iMac soon (first Apple computer in general, really); I was originally going to get the last model since I'm in dire need of a desktop, but since we're already in the new year, I decided to just wait it out for the new one. I'll most likely be getting the cheaper entry-level model. My question is, is an iMac upgrade-able should what I get not satisfy my needs? I understand that RAM is upgrade-able but that's all I know.