At its Build 2017 developer conference today, Microsoft announced that Windows 10 is now on over 500 million devices. It took the company’s latest and greatest operating system about 21 months to hit that milestone.

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, and 400 million after 14 months. Microsoft was aiming for 1 billion devices running Windows 10 “in two to three years,” but backpedaled on that goal.

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 naturally flattened over time.

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

  • Windows 10 was available as a free upgrade for Windows 7 and Windows 8.1 users during its first year. This is why Microsoft counts “active devices” and “ac with Windows 10 rather than “license sales.”
  • While its phone business is basically dead, Microsoft is still counting phones running Windows 10 Mobile (both purchased and those that have upgraded) in the total figure. Xbox Ones, Surface Hubs, and HoloLens devices are also included.
  • With every subsequent Windows release, there are more computers and people in the world. The pie has grown, so the potential number of devices that can be running Windows 10 is larger than for its predecessors.

Windows 10 is a service, meaning it was built in a very different way from its predecessors so it can be regularly updated with not just fixes but new features, too. Microsoft has released many such updates, including three major ones: November Update, Anniversary Update, and Creators Update.

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