check in windows system drive management. look to see what drive has the windows system partion on. it a hidden restore partion of a set size when you install windows. then there the windows swap file. there can also be a hibernation file. and some of the system restore points. (clear out the restore points if you want to but if you have a crash you wont have a way to go back with windows.). also 2tb drive with formating your going to lose some space to the format. most vendor should put the format size on the drive.