Microsoft’s latest operating system is really popular.

The company on Jan. 4 announced that Windows 10 is now running on 200 million devices worldwide, up from 75 million in August 2015. Perhaps more surprisingly, Microsoft has nearly doubled its Windows 10 adoption since October, when it announced it had registered 110 million activations.

Microsoft launched Windows 10 in July 2015. Unlike its previous launches, Microsoft offered the operating system for free to all Windows 7 and Windows 8 users, including those who had pirated copies of its earlier platforms. If the freebie offer wasn’t enough to coax customers into going with the operating system, Microsoft also brought back several features it unceremoniously ditched in Windows 8, including the popular Start Menu. Windows 10 also added extra security features that caught the attention of business customers.

It was Microsoft’s decision to offer Windows 10 for free, however, that proved most controversial. The company has long charged consumers to get new versions of its software, but CEO Satya Nadella decided against the old tack. Instead, he reasoned that getting more people into Windows 10 would ultimately benefit all facets of his business. More specifically, he has argued that the more people who adopt Windows 10, the more likely they’ll be to use Microsoft’s other platforms, including cloud-based services, like Office 365 and Azure.

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Along the way, Microsoft has argued that it could reach a billion Windows 10 activations by the summer of 2018. So far, the company claims, it’s on its way.

In addition to announcing 200 million devices are now running Windows 10, Microsoft said that the operating system has “the fastest growth trajectory of any version of Windows ever.” Indeed, Windows 10’s adoption rate is 140% faster than Windows 7 at the same point in that platform’s lifecycle. Windows 10 is outpacing Windows 8 by nearly 400%, Microsoft says.

Windows 10 usage has been particularly high in recent months. Microsoft says that approximately 80 million Windows 10 devices were activated since Black Friday. In December, alone, Windows 10 notched more than 11 billion hours of usage, according to the company’s statistics. Since the operating system’s launch, Cortana, Windows 10’s personal virtual assistant, has responded to over 2.5 billion questions.

WATCH: For more on Windows 10 reviving Microsoft, check out the following Fortune video:

While Microsoft has, of course, touted Windows 10’s success, Daniel Ives, an analyst at FBR & Co., says that it should. He said in a note to investors on Monday that 200 million activations is a “white hot number,” and shows clearly that Windows is “firing on all cylinders.”

“While many on the Street have fretted about the free-upgrade strategy, arguing the expiration-driven cycle will only provide a one-time benefit for Microsoft (and its investors), we believe this remains the ‘only way to go,’ as Nadella needs to drive mass adoption across consumers and enterprises with the underlying goals of creating a more consistent platform experience and attracting an increased number of developers/apps for its mobile offerings and devices,” Ives wrote.

MORE: Here’s How Many People Have Installed Windows 10 Already

Looking ahead, Ives expects similar success from Microsoft, saying that the company’s “lofty” revenue goals now look “within reach.”