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Microsoft is announcing Monday that Windows 10 is now running on more than 200 million devices, up from 110 million in October. The software giant bills it as the fastest takeoff for any Windows version ever. But in many ways, the milestone serves to highlight how much work remains.

First off, even on the numbers, Microsoft has set an audacious target, promising to have Windows 10 active on a billion devices within three years.

Beyond the numbers, though, Microsoft still has to convince mobile developers who have grown up on iOS and Android to add Windows to their must-have list.

There’s also the image issue. Windows’ prestige has taken a beating in recent years as Apple managed to become synonymous with sleek and simple. Microsoft has regained some ground with its homegrown hardware, turning around losses from Surface and receiving critical acclaim for the Surface Book, the first Microsoft-made laptop.

The gains also highlight the strongest thing on Microsoft’s side — the fact that a whole heck of a lot of Windows PCs continue to be sold. And since the same apps can run on Windows 10 PCs and on Windows phones, Microsoft’s battle for phone apps could get easier in the years to come.

Also of note, Microsoft says Windows 10 usage is outpacing prior versions and the app store is generating four times as much revenue for developers as was the case with Windows 8.

That operating system was largely panned by users, who showed their displeasure with the new interface by spending more time in classic mode than running new-style Windows apps. Windows 10 aims to blend the new and the familiar, bringing back the start menu and allowing new-style Windows 10 apps to run alongside classic programs.

Microsoft threw out a bunch of stats on Windows 10, noting that there have been 44.5 billion minutes spent in the new Microsoft Edge browser and 2.5 billion questions asked of Cortana, Microsoft’s answer to Apple’s Siri.

“Overall, we are seeing significantly higher customer satisfaction with Windows 10 than any prior version of Windows,” Microsoft’s Yusuf Mehdi said in a blog post.