from the wikipedia article: http://en.wikipedia.org/wiki/ExFAT
Microsoft has not released the official exFAT file system specification, and a restrictive license from Microsoft is required in order to make and distribute exFAT implementations. Microsoft also asserts patents on exFAT which make it impossible to re-implement its functionality in a compatible way without violating a large percentage of them. the article links a pdf with some reverse engineered info. that should be enougth to implement it. the principle is the same as fat. but its not clear how one can get this license from microsoft. -- cinap
