whether i'll be a fan, processors or various heatsinks, how can you know which ones to buys just in case? example, xp fans may carry certain volts, heatsinks come in different sizes, do processors come in different sizes? what about any graphic cards? only reason why i'm asking because i was sanding one of my xp processors and accidently erase the markings of it. does the markings have something to do with a certain model of a certain computer? also i wanna learn of bying things becuase cpu's can get pretty costly.