We can categorized view of Operating System:
(i) User View: It various according to the interface being used. User interface with monitor, keyboard, mouse and system unit. They uses for maximize the work that the user is performing. OS provides the services, execution of program, control access to files, access to I/O devices, error detection etc.
(ii) Hardware View: According to hardware view OS acts as resources managers, e.g. allocation of resources, protection of resources etc.
(iii) System View: Operating System is the program most intimately involved with the hardware. It is set of instructions that are executed by the processor.