"iOS 7 is the seventh major release of the iOS mobile operating system designed by Apple Inc as the successor to iOS 6. It was announced at the company's Worldwide Developers Conference (WWDC) on June 10, 2013, and was released on September 18, 2013. iOS 7 includes a redesigned user interface and numerous functionality changes. The design of iOS 7's new elements was led by Jony Ive, Apple's Senior Vice President of Design. As of February 2014, iOS 7 has been installed on 82% of supported devices. The most recent update, 7.1, was released on March 10, 2014."
You can see the list of supported devices with this link: