Operating system goes by many different names, depending on the manufacture of the computer, other terms used to describe the operating are: monitor, executive, supervisor, controller and master controller programs.

An operating system (sometimes abbreviated as "OS") is the program that, after being initially loaded into the computer by a boot program, manages all the other programs in a computer. The other programs are called applications or application programs. The application programs make use of the operating system by making requests for services through a defined application program interface (API). In addition, users can interact directly with the operating system through a user interface such as a command language or a graphical user interface (GUI).

Today most operating systems perform the following functions:

1. Processor management i.e. assignment of processors to different tasks being performed by the computer system.

2. Memory management, that is, allocation of main memory and other storage areas to the system programs as well as user programs and data.

3. Input/output management that is coordination and assignment of different input and output devices while one or more programs are being executed.

4. Automatic transition from job to job as directed by special control statements.

5. Maintenance of internal time clock and log of system usage foe all users.

6. Facilities easy communication between the computer system and computer operator.

An operating system performs a wide variety of jobs. Each of jobs are performed by one or more computer programs and all the computer programs and all the computer programs are jointly known as an operating system. Out of the complete operating system, normally, one control program resides in the main memory of the computer system. This control program is known as the residential program or resident routine. The other programs are stored on the disk and are called transient programs or transient routines. The control programs transfers these programs in to the main memory and executes them as and when they are need. It may be recalled here that the capacity of the main memory of any computer system is very small as compared to its secondary storage devices. This is the reason why only the control program is stored in main memory and the rest of the operating system is stored on disk.

The effect, besides the hardware, each computer system consists of an operating system that enables a user to effectively use the system.The operating system tends to insolate the hardware from the user. The user communicates with the operating system, supplies application programs and input data, and receives output results.