Windows 10 will have different modes depending on the screen size it runs

Microsoft to unify the Windows Shell across Phones, PCs and Xbox
Microsoft is working on an adaptable Shell for Windows 10, according to Windows Centrаl. Future updates for PC, Mobile and Xbox will introduce the improved Windows environment that scales across different form factors. Consider this as an evolution of Continuum that gives us the features we need at any time.
The software giant is planning to bring the new Windows Shell to all devices over the next few Windows 10 Updates, offering us a real unified Windows experience.
Currently, Windows 10 and Windows 10 Mobile have individual shells updated separately. In the near future, Continuum will work not just between PC and tablet, but Windows will also scale across phones and gaming consoles. The new ‘Composable Shell’ will scale in real-time across form factors, which means the user may instantly switch between phone and desktop mode when the phone is connected to a bigger screen.
Microsoft already hinted about the upcoming Desktop environment to Windows 10 Mobile, showing an improved Continuum with re-sizable app windows.
What does the Composable Shell mean for Windows Phone?
Windows 10 Mobile and Windows 10 will have far more common things in the future. In fact, both versions of Windows will be just two of the modes thanks to the new shell.
Future devices with screens up to 6 inches may still be called ‘Phones’, but they will be real Pocket PCs, providing both a phone and a desktop experience depending on the situation. Furthermore, with Microsoft patenting a foldable phone, we may even have a 3-in-1 device – a phone, tablet and PC (connected to external display).
Microsoft may give more details about its plans for the Windows ecosystem in the BUILD 2017 conference this Spring.