In strict literary terms, An Operating System refers to “the low-level software that supports a computer’s basic functions, such as scheduling tasks and controlling peripherals.” In simple words, an operating system is a system of commands which controls the operations of the CPU and devices attached to it. It is the first and the most important program that runs on a computer. The computer gets started only when the operating system starts. Other programs and applications run only when an operating system runs successfully. Right from the input from keyboard to the output on monitor or printer, all are under the control of an operating system.