Where are you getting these ideas from. Or rather the HD space count?
If you go to My computer and click drive C or local disk it will tell you how much is on your drive.
From that you subtract from the 200gb and you get 200gb. Or add it back up. See what im saying?
When you put a OS on a new hard drive it takes up space. When you add files and software it takes up space.
My pc has a 30gb HD in it and it says it has 27.7 total. It says this in My computer. Here is a snapshot I took to show you:

This is normal but if you have no files on it yet but have the OS it still is going to say a little off.
Put it this way it always has for me. I think its normal I could be wrong but why you are losing almost 12gb of your 200gb HD is puzzling....
Hope this has helped you out some.