At Microsoft’s annual shareholders meeting today, CEO Satya Nadella announced that Windows 10 is now on over 600 million monthly active devices. It took the company’s latest and greatest operating system about 27 months to hit that milestone, as first reported by GeekWire.

Windows 10 was installed on over 75 million PCs in its first four weeks, passed 110 million devices after 10 weeks, 200 million in under six months, 270 million after eight months, 300 million after nine months, 350 million after 11 months, 400 million after 14 months, and 500 million after 21 months.

Microsoft was aiming for 1 billion devices running Windows 10 “in two to three years,” but backpedaled on that goal. The company is inching closer to 1 billion, but at this rate, we would estimate 2020 as the likely timeframe.

Here’s the progress in a chart, with Windows 7 and Windows 8 thrown in for context (Microsoft stopped reporting Windows 8 milestones after 200 million):

As you can see, Windows 7 and Windows 8 milestones were similar for the first six months or so, though it quickly became clear that Windows 8 was not selling as quickly as its predecessor did. Windows 10 has been ahead of both from the start, though its slope has expectedly flattened just as previous versions have.

Windows 10 adoption is faster than that of its predecessors for a number of reasons. Here are the three big ones:

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