This question must have been hundreds times, but please help. I want to know what the Microsoft policy is concerning licensing its softwars. In particular: 1) I need to alternate two or three hard drives in the SAME computer depending on the kind of work I do. The platform installed in my current routine hard drive is Win XP Pro which is 'genuine' with legitimate product key. When it was activated, I believe, Microsoft collected information specific to this particular hard drive product together with discriminatory information about the computer's hardware set up (motherboard, memory card, CPU, graphic card, etc). Now, if I replace the hard drive and install the same OS from the SAME CD (with the same product key) followed by going through new activation process, I am sure that the activation attempt will pass (because the OS software is 'genuine'). Then, when I switch back to the previous harddisk in which the same OS with the same product key has been installed, what will happen? Will it work without complication? Or will it need to go through another activation and safely? (I will not and will not be able to use the two drives simultaneously.) If so how many times will I be permitted to do such a switching if there is a limit to it? (Does information about successful activation stay inside the disk or is it in MS's activation database and checked out every time the disk is used?) 2) If I install the same OS in a deifferent partition in the same hard drive and use it in the same computer, what will happen? My thought: What Microsoft wants is prevention of a software from its use in "different computers" at the same time, isn't it? That is, MS does not want piracy. When we purchase a "genuine" MS software, however, we own it with every right of the ownership and we should be able to use it in every way we want as long as we do not commit piracy or illegal transaction, right?