HDD Free Space Discrepancy

Now I’m not the brightest person out there but according to my math theres 200 Gig’s unaccounted for The MyCloud is showing 2.2TB free and when its mapped as a drive its showing 2.0TB. Can someone tell me whats going on here? Is this maybe a windows limitation?

Windows Math.

WD is reporting in Terabytes  (1TB = 1,000,000,000,000 bytes)  (Using decimal multiples.)

MS is reporting in what’s commonly known as Tebibytes (1TiB = 2^40 = 1,099,511,627,776 bytes, using Binary multiples.)

2.2 TB = 2.0 TiB.

http://en.wikipedia.org/wiki/Tebibyte