I'm thinking of buying a used 60GB Playstation 3 locally (not sure if this is a good idea). Is there a way to externally identify what version a PS3 is? I think I can rule out the 20 and 40 if it has 4 USB ports and a flash card reader, but not the 80. Are the different versions segmented into different serial number prefixes? Is there text somewhere on the bottom that tells you? And where should I look when the system is plugged in? I'm trying to be as paranoid as I can with this.