I got my notice to reserve Windows 10. I'm running Windows 7. I did read an article that Windows 10 will be the last version of windows.
http://www.forbes.com/sites/antonyleather/2015/05/08/windows-10-to-be-last-version-of-window
It will constantly update.
Windows 10 Home: The consumer-focused desktop edition.
Windows 10 Mobile: The re-branded Windows Phone for smartphones and tablets.
Windows 10 Pro: A desktop edition for PCs, tablets and 2-in-1s aimed at small businesses.
Windows 10 Enterprise: Builds on Windows 10 Pro with added advanced features designed to meet the demands of medium and large sized organisations.
Windows 10 Education: Designed to meet the needs of schools with academic Volume Licensing.
Windows 10 Mobile Enterprise: Designed to deliver the best customer experience to business customers on smartphones and small tablets.
Windows 10 IoT Core: Windows 10 for other devices and machines such as ATMs and handheld terminals.
Windows 10 Mobile: The re-branded Windows Phone for smartphones and tablets.
Windows 10 Pro: A desktop edition for PCs, tablets and 2-in-1s aimed at small businesses.
Windows 10 Enterprise: Builds on Windows 10 Pro with added advanced features designed to meet the demands of medium and large sized organisations.
Windows 10 Education: Designed to meet the needs of schools with academic Volume Licensing.
Windows 10 Mobile Enterprise: Designed to deliver the best customer experience to business customers on smartphones and small tablets.
Windows 10 IoT Core: Windows 10 for other devices and machines such as ATMs and handheld terminals.