The rules appear to have changed a little - I bought an OEM copy from Newegg and bought NO additional hardware. However an OEM copy is for a "Builder", to put on a machine built by someone else for an end user. That copy is specific to the machine it is originally installed on, not to be moved to another machine later, with a label that is supposed to be affixed to the machine(Mine is on the inside of the battery bay). The retail copy is Stand-Alone and can be installed on any machine as long as only one copy is installed and running at a time. Also, the OEM copy has NO Tech Assist from the seller or M$. Returns are difficult(my first copy was no good, they sent a second that worked), refunds next to impossible. If I had known all this, I would have spent the extra dough for the retail copy...Z