Microsoft has really ambitious plans for Windows 10.
Speaking on stage at its Build 2015 conference, Terry Myerson, Microsoft's executive vice-president of operating systems, said he wants to see 1 billion devices running Windows 10 within two to three years.
In comparison, Android 4.4 "KitKat" is on around 500 million devices. iOS (presumably iOS 8) is on even fewer devices, Myerson said.
"With Apple, you choose to invest in iOS and OS X. With Google, it's Android or Chrome OS," Myerson said. "Windows is the only platform that lets you bring apps to all these devices efficiently."
"To make all this worthwhile for developers, we know we need to get Windows 10 broadly adopted quickly."
Windows 10 will be available as a free software update for the first year to Windows 7 and 8 users later this summer.