My iMac 24 has been acting just a tiny bit sluggish of late, seeing the pinwheel a few times. All the reading I've gone through suggests two possibilities; overloaded cache or a HDD that's starting to go south. Hmmmm. OK, so exactly how do I get to the so-called "Library Caches" and which folders do I delete. Next, is there a good diagnostic tool that will give me layman's language results that a consumer/user can understand? And lastly, if the HDD is going south and my iMac is long past warranty... can I; (A) replace the HDD myself, and (B) can I upgrade the drive size (currently 500G) to a 1TB drive? My machine currently has 4 Gigs of RAM and I guess that's all it can handle right? Wish I could upgrade that! I did clear my safari cache and saw a decent pickup in speed.