Microsoft has revealed that sales of its Surface tablets totalled $853m (£562m) in their first eight months on sale.
The figure suggests the company may struggle to make a profit out of the product.
It has booked a $900m write-down on the value of unsold Surface RT stock after cutting the device's price.
Its latest financial filing also notes that its advertising budget swelled to promote the machines.
The filing says the Windows Division's sales and marketing expenses were $843m higher in the firm's last financial year than the previous one because of the launch of the Surface tablets and new Windows operating systems.
http://www.bbc.co.uk/news/technology-23520010