It is a program that acts as an interface between the user and the hardware (i.e. for all computer resources). An operating system is an important component of a computer system, which controls and co-ordinates all other components of it. It activates all devices that makes them ready for work. It also performs all internal management functions and ensures systematic functioning of a computer system.The operating system performs the following functions:1. It recognises input from keyboard and sends output to the display screen.2. It makes sure that the programs running simultaneously do not interfere with each other.3. It is also responsible for security, ensuring that unauthorised users cannot access the system e.g. MS-DOS, Windows 95, Windows XP, Windows Vista etc.