OnePumpChump is correct, its about making more money. The Home versions are only licensed for a single die (chip), and so it will only recognize however many cores you have on a single chip (I have a "quad core", which is really two Xeon chips, each with two cores). Interestingly enough, the Vista DVDs contain ALL versions of Vista (of the same bit variety, meaning all x32 bit versions or all x64 bit versions). It is the license key that determines what "version" (feature functionality) is loaded/enabled. To enable multiple dies (chips), you need the Enterprise or Ultimate version.