Mac OS is a series of graphical operating systems developed by Apple for their Macintosh computers. The first Mac OS was introduced in 1984 with the original Macintosh PC. Over time, Apple developed newer versions that introduced significant new features and graphical overhauls, including Mac OS X in 2001 which transitioned to a UNIX-based system. The latest version is OS X Yosemite which was released in 2014 and brought design inspiration from iOS 7 while maintaining the OS X interface.