
Operating system is an intermediary between computer user and computer hardware, it acts as an interface between user and hardware. It resides in upper portion of main memory and works in privileged mode. Functions of OS are: file management, memory management, device management and process management. Goal of OS are: convenience (eg. Windows OS) and efficiency (eg. Unix). Generations of OS are: 1.sequential,
2.Batch,
3.Multiproggramming,
4.Real time OS.