Windows Phone 7 was the first and previous release of the Windows Phone mobile client operating system, released worldwide on October 21, 2010, and in the United States on November 8, 2010. An update to the OS codenamed Mango (also referred to as Windows Phone 7.5) was released in May 2011. In January 2013, Windows Phone 7.8 was released. It added a few features backported from Windows Phone 8, such as a more customizable start screen.