The interface between hardware and a user. It is responsible for the majority of computing functions, mainly: Starting up/turning off the system, executing programs, executing services/tasks. Microsoft's Windows & Apple's Mac are both examples of operating systems. Operating Systems are also used on Lighting Consoles, for example, EOS/ION use there own specially designed OS. Strand's 300/500 range use MS DOS as there OS and the interface is simply an application.