Need of operating system:

What kind of facilities operating system provides to the users and programs:

• The operating system provides interfaces for the user (keyboard, mouse, clicks, and pen drive) and also for the user's programs.

• It provides file system support to manage huge volume of data in to secondary storage device.

• It provides I/O services that can be used by every program.
• It provides  boot-strapping  or  Initial Program Load (IPL) to start a computer

• It manages all kinds of errors  and also supports error recovery mechanisms 
• It provides networking services.
• It provides the environment (allocation of memory, I/O devices and CPU time)  for  concurrent processing.  As you are aware, a single processor is capable of executing only one instruction at a time. Concurrent processing is the means used to simulate the simultaneous execution of multiple programs to provide multitasking and multiuser support.