Microsoft's Surface tablets have not made any any profit as slow sales have been eclipsed by advertising costs and an accounting charge, according to the software company's annual report. The two SUrface tablet models have so far brought in revenue of $853 million, Microsoft revealed for the first time in its annual report filed with regulators on Tuesday. That is less than the $900 million charge Microsoft announced earlier this month to write down the value of unsold Surface RT.

Microsoft said its sales and marketing expenses increased $1.4 billion, or 10 percent, because of the huge advertising campaigns for Windows 8 and Surface. It also identified Surface as one of the reasons its overall production costs rose.