iPhone OS 1, commonly referred to as iOS 1, is the first major release of iOS, Apple's mobile operating system. No official name was given on its initial release; Apple marketing literature simply stated that the iPhone runs a version of Apple's desktop operating system, macOS, which used to be known as Mac OS X. On March 6, 2008, with the release of the iPhone software development kit (iPhone SDK), Apple named it iPhone OS (they later went on to rename it "iOS" on June 7, 2010). It was succeeded by iPhone OS 2 on July 11, 2008.