What is Operating System ?

An operating system or OS is a software program that enables the computer hardware  to communicate and operate with the computer software . Without a computer operating system, a computer and software programs would be useless

When computers were first introduced the user interacted with them using a command line interface, which required the user to perform a series of commands in order to interact with the computer and its hardware and software. Today, almost every computer is using a Graphical User Interface (GUI) operating system that is much easier to use and operate.

Operating systems can be classified as follows :

Multi-User         : Allows two or more users to run programs at the same time. Some  operating systems permit hundreds or even thousands of concurrent users.

Multiprocessing  : Supports running a program on more than one CPU.

Multitasking       : Allows more than one program to run concurrently.

Multithreading    : Allows different parts of a single program to run concurrently