Most usually laptops have a separate partition where the installation is preserved, thus you do not need a separate disc - or, the computer comes with a separate disc. Unfortunately, some "business men" duplicate Windows, selling something that's functional, but not really legal.
If you want to have it working, you mention it in your opening post - which I do not, definitely, support. If you want it to be legal, there's only one address: Microsoft. That's the ballgame.