Microsoft filed its annual Form 10-K with the Securities and Exchange Commission (SEC) on Tuesday, revealing the exact amount of revenue from its Surface efforts: $853 million. The figure covers revenue from when the Surface RT launched in October through to the end of June, and the company's Surface Pro sales too. It's less than the recent $900 million write-down for Surface RT that the company revealed in its latest quarterly earnings, and as GeekWire points out it's also less than the "$898 million increase in advertising costs associated primarily with Windows 8 and Surface."

Microsoft doesn't reveal Surface sales figures in its SEC filing, but based on the revenue the initial reports of Surface RT sales at 1.5 million units in March, and Surface Pro at 400,000 could well be accurate. The software maker has been forced to cut the price of its Surface RT tablets by 30 percent worldwide in an effort to sell more of the devices. CEO Steve Ballmer recently admitted the company had built too many Surface tablets, and that it's not selling as many Windows devices as it wants to. Microsoft is expected to refresh both of its Surface RT and Pro tablets later this year, and the company has been hinting at additional accessories as part of those efforts.