When Windows 10 was launched—and when Windows on phones was expected to add tens of millions of devices—Microsoft set itself a target of one billion devices within two to three years.
If it can continue to grow at 100 million devices every six months, then the one billion target should be about a year away. There’s a good chance that the growth rate might actually tick up over the next year, due to Windows 7’s impending end of support. In nine months, the operating system released in 2009 will drop out of free support (though paid support options will remain), and many hundreds of millions of corporate users are still using it. While some users will inevitably keep with what they know, most are likely better served by upgrading.