"Once a device is upgraded to Windows 10, we'll be keeping it current for the supported lifetime for the device," said Terry Myerson, chief of Microsoft's operating systems division.

All customers running Windows 7, Windows 8.1 and Windows Phone 8.1 will be able to upgrade to Windows 10 for free within a one-year period following the operating system's launch later this year. After that period, users will have to pay for the upgrade as they would have with previous versions of Windows. Those who get the upgrade during the free period will have Windows 10 on their device permanently.