Some people have bought the Microsoft Surface tablet thinking they were getting Windows 8 when they really got Windows RT. So what’s the difference? Windows 8 is a full OS like you would have on any laptop or desktop. Windows RT is a mobile OS that works with apps rather than programs. If you want a full Office Suite on your tablet, then you want Windows 8, but if you can settle for an app, you can use Windows RT. Some other differences are price, size, weight, thickness, connectivity. You can find a full comparison chart here.
So depending on what you want to use a Surface tablet for, you can find the correct one to purchase.