It is the system I.D. from what I understand, not the hard drive. If it was the hard drive you could just move the drive to another system or even use something like Norton Ghost to copy it. You should be able to use the same number even if you format your drive and start over. My computers are all built ground up by me, and I am still able to use these types of copy protection even after formatting my drives, which I do frequently due to the crap that accumulates. Someone correct me if I'm wrong. Marque