Windows Phone 8 is the second generation of the Windows Phone mobile operating system from Microsoft. It was released on October 29, 2012, and like its predecessor, it features a flat user interface based on Metro design language. It was succeeded by Windows Phone 8.1, which was unveiled on April 2, 2014.
Windows Phone 8 replaces the Windows CE-based architecture used in Windows Phone 7 with the Windows NT kernel found in Windows 8. Current Windows Phone 7 devices cannot run or update to Windows Phone 8 and new applications compiled specifically for Windows Phone 8 are not made available for Windows Phone 7 devices. Developers can make their apps available on both Windows Phone 7 and Windows Phone 8 devices by targeting both platforms via the proper SDKs in Visual Studio More: en.wikipedia.org.