A brand new computer will always come with a back-up disc. But it doesn't JUST have the OS on it most of the time. It usually comes with extra programs such as IE, Windows media player, Acrobat reader stuff like that. Programs which they think you will need on the computer. If it doesn't come with a back up cd then you will have to complain, and they will send out another one. The only way you wouldn't get a back up cd is if you created a computer yourself with your own parts. Then you'd have to buy the OS disc itself.