If you exclude non-Windows operating systems, Windows 10 is now 21.32% of the Windows market, a mark it took 11 months to hit. And while that may look like a lot when compared to previous versions of Windows, you need to remember that previous versions of Windows were not being given away. Microsoft had never given away a new OS prior to this one, which makes sense when you remember that they are primarily a software company. Windows and Office are their two main breadwinners.
Comparing Win10's adoption rate to that of previous versions of Windows is like comparing bowling balls to tennis balls. Yes, they're all balls, and they're all used for sports, but if you try to play tennis with bowling balls (or vice versa) you'll figure out pretty damn quickly that they're fundamentally different things.
In order to get a meaningful comparison, you'd need to compare Windows 10's adoption rate to that of another OS that gives new versions away. Fortunately, there is one: Apple's OS X.
Apple is not a software company; they're a consumer electronics company. They've always made their money from selling hardware, much like Panasonic, Samsung, or Sony, and they've never allowed OS X to be installed on non-Apple PCs; the Apple OS is part of their brand, so exclusivity is a feature and not a bug. So it made sense when, three OS versions back, Apple started providing OS upgrades to their Mac customers free of charge.
The most recent such update was OS X 10.11 El Capitan, released last fall, and it was a hit with Apple's customers: just over a month after release, El Capitan was running on 27% of Macs.
From Computerworld:
Apple's OS X El Capitan in October got off to the fastest-ever one-month start for a Mac operating system.
El Capitan, also tagged by Apple as OS X 10.11, was released on the last day of September: 31 days later it had been installed on another 25% of all Macs, bumping its total to 27%, according to U.S. analytics firm Net Applications.
The October increase was the largest one-month user share gain by an edition of OS X in the six years that Computerworld has recorded Net Applications' data, beating Mavericks and Yosemite, the two previous upgrades Apple handed out free of charge.So, when Apple gives away a new version of OS X, it gets adopted by 27% of all Mac users in a single month. Microsoft, by comparison, has taken 11 months to reach a mark of just over 19%. Yes, that is 350 million PCs; it's faster adoption than they've ever produced by selling copies of each new Windows version, and it's almost certainly faster than they could have achieved by selling Windows 10 like they always had before, but still... only 19% in 11 months, when you're giving the shit away for free? That's not an impressive showing.
Microsoft's corporate strategy requires Windows 10 to be installed on a billion PCs within two years. Given that it's taken them 11 months to fall short of a new OS adoption mark that Apple can reach in a month with OS X, and with only 13 more months to go, I'm having serious doubts about their ability to get there.