Windows RT with Office and essential apps on the Surface takes up a whopping 12GB, according to members of Microsoft’s Surface team.
Answering a question about how much space Windows RT occupies, Ricardo Lopez, a test manager on the Microsoft Surface team said he had nearly 20 GB of free space with Windows RT, Office RT, and "a bunch of apps."
So while we can't exactly say how much Windows RT takes up, fact of the matter is that you should get around 20GB of free space. And that's not much more than the nearly 14GB of free memory on the 16GB iPad.
And that explains why you don’t have a 16GB Microsoft Surface - it simply wouldn’t have enough space for storing things outside the operating system.
And that’s what bothers us. The Surface is already up for pre-order but important details like this one are only now appearing and not even through the official channels. We wouldn’t rush to get it until we know all the final details - it does seem like a beautifully designed product, but we know little more than that.
source: Reddit via Business Insider