I am looking to buy a used 24" iMac - and the one I have found is an early 2008 with a Core 2 Duo 3.06GHz processor, 4GB RAM, and 640GB hard drive. I don't believe it can be upgraded to Sierra OS (It has El Captain 10.1) and I believe 4GB is teh max amount of RAM it can handle. Also, can it handle a bluetooth keyboard/mouse? What should I be looking for before I buy this, and how much should I spend on a unit like this? Condition is almost perfect. Not going to be doing any resource intensive tasks on the PC just watching movies and surfing the web.