Well this is quite the change for Microsoft. They have decided to offer Windows 10 as a free upgrade for existing users of Windows 8.1 and Windows 7. This offer will only be available for the first year following the release of Windows 10.
After the first year users of Windows 7 and Windows 8.1 will have to pay to upgrade to Windows 10. This seems like a great way to get adoption of the operating system off to a fast start. Windows 10 wil bring back the Start Menu, a productive Desktop environment, and cutting-edge new API features like DirectX 12.