Microsoft has announced that cumulative sales of Windows 8  including brand new machines running the OS and upgrade licenses for existing devices  have hit 60 million.In post made on the company's Windows blog, Microsoft communications manager Brandon LeBlanc said the firm's in-house numbers suggest the new OS is currently enjoying a "similar sales trajectory" to that of Windows 7."We have seen a significant increase in the number of Windows 8 certified systems since general availability at the end of October," added LeBlanc."There are now more than 1,700 certified systems for Windows 8 and Windows RT."The news comes as the spotlight is cast upon both Windows 8 and Windows RT at CES 2013 in Las Vegas, with Qualcomm having devoted a portion of its keynote at the event to showcasing Windows RT tablets and Windows Phone 8 devices from Nokia and HTC  all equipped with Snapdragon processors.More important for developers, however, is Microsoft's assertion that the Windows Store  which pushes apps across both Windows 8 and Windows RT  is taking off."This week we also highlighted strong growth in developers building for Windows 8," concluded LeBlanc."Since the opening of the Windows Store the number of apps has quadrupled and we passed the 100 million app download mark  just two months after general availability."[source: Microsoft