Windows 10 is now on more than 300 million active devices, according to numbers released today by Microsoft. It continues to be the most rapidly adopted version of Windows ever. At the end of March, Microsoft said that the operating system had hit 270 million active users.

The Windows 10 release is, of course, unlike any past version of Windows in two important ways. First, the operating system was released as a free upgrade for many users of Windows 7 and Windows 8. Second, the operating system is offered as a regularly updated "service"; rather than waiting years for a new version of Windows before new features can be added, Microsoft is adding new capabilities in periodic updates. The next of these, the Anniversary Update , is due this summer and will add richer pen/stylus support, the ability to run some Linux programs natively , and extensions to the Edge browser.

Microsoft's original stated goal was to have 1 billion Windows 10 users within the first two to three years. At the current rate of adoption, this seems plausible, though sustaining the current uptake rate over three years will be a challenge. Making this harder is the imminent demise of the free upgrade program. After July 29, upgrading from Windows 7 or 8 to Windows 10 will cost $119.

There is some skepticism that Microsoft will in fact follow through on this. Making Windows 10 a conventional paid upgrade is going to make that one billion system target much harder to reach; Windows 7 is the most widely used version of Windows by a considerable margin, with Windows 7 users outnumbering Windows 10 users by about three to one, indicating that there is still a substantial number of people who have not taken advantage of the free Windows 10 upgrade. While many of these are likely to be enterprise users who aren't eligible for the free upgrade anyway, there is sure to be a good number of home users still running Windows 7.

While the end of the free upgrade program will certainly provide some impetus to make the upgrade, we wouldn't be terribly surprised to see Microsoft come up with some way of extending or renewing the scheme at the eleventh hour.