a system builder disc is a oem type key kind of like a coa key. it can not be auto activated and is tied to one machine. with one of these any major changes in hardware will usually result in a need to re activate. and most of the time after one or two online activations you will need to use the phone method. just remember to tell them this is THE ONLY system its installed on and also i usually tell them the motherboard went bad or the hard disk failed so i had to reinstall it. they will re activate online.