An Operating System is a program that acts as an intermediary between a user of a computer and the computer hardware. Objectives of Operating System are: Convenience: - for small PC’s. Efficiency: - for large, shared multi user systems since they are expensive. Ability to evolve The OS controls and coordinates the use of hardware among the various application programs for various users. OS is like a government. Like government, it performs no function by itself. It simply provides an environment within which other programs can do useful work. OS is a Resource Allocation.