You installed Windows to the entire drive. So, the entire drive is reserved for whatever you do in Windows 7. You can create a partition and install Vista, XP, Linux, or store data on that partition. So, a partition is basically like having multiple HDD's. Also, it is never recommended to backup your drive to itself, e.g. backing up your files to the same HDD/partition. If you get a virus/HDD crashes, you will lose the data+backup. So, get an external drive an backup to that.