Windows Phone 7 (WP7) is the first release of the Windows Phone mobile client operating system, released worldwide on October 21, 2010, and in the United States on November 8, 2010. It runs on the Windows CE 6.0 kernel. It serves as the successor to Windows Mobile 6.5.
Windows Phone 7 was a complete overhaul of Microsoft's previous mobile Windows platforms. It was designed with the distinct flat-styled Metro interface. Due to shell changes, Windows Phone 7 cannot run Windows Mobile 6 applications. The first major update to Windows Phone 7 was Windows Phone 7.5, codenamed "Mango", which was globally released on September 27, 2011. Windows Phone 7.x was succeeded by Windows Phone 8, which was released on October 29, 2012; existing Windows Phone 7.x hardware could not upgrade to the incompatible Windows Phone 8 software. As a compromise to existing users, Microsoft released Windows Phone 7.8 on January 31, 2013, adding a few features backported from Windows Phone 8, such as a more customizable start screen and the new bootscreen.