In Windows Phone 7, the operating system was based on Windows CE, which was the operating system for small devices, but different from the OS that covers the big Windows.
When Microsoft launched Windows Phone 8, they swapped out the Windows CE operating system and based it on the Windows NT kernel. This was the same for PCs and Xbox One.
But with Windows 8.1 and Windows Phone 8.1, Microsoft delivered it on a converged developer platform with the option to build applications targeting the universal 8.1 app platform that shares a high percentage of the code.
With the launch of Windows 10, it changed again. The code has been improved further and generalized to provide a single set of APIs to create a single app which can run on all device families running the Windows 10 operating system. They named it Universal Windows Platform (UWP...
