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Operating System is a resource manager which manages all the resources of computer. It is a system software whose main objective is to make the computer easy to work. Normal user can not work with out operating system. It is a interface between use and computer hardware.

An operating system is a program that is an intermediary between a user and the computer hardware. Different levels in a computer system are shown below (Figure 1.1).

Levels in a computer system

An operating system provides an environment in which a user can execute programs. The purpose of an operating system is two fold:To make the computer system convenient to use. To use the computer hardware in an efficient manner.

What is an Operating System

An Operating system is a software program that controls the execution of application programs and acts as an interface between the user of a computer and the computer hardware.

Function of Operating System

An Operating system mainly performs three functions –

Convenience : It makes computer more convenient to use

Efficiency : It allows the computer system resources to be used in an efficient Manner.

Ability to solve: It should be constructed in such a way as to permit the effective development, testing and introduction of new system functions without at the same time interfacing with service.

Services of Operating System

The Operating system typically provides services in the following areas :

Program Creation: Operating system services editors and debuggers, to assist programmer in creating programs.

These services are in the form of utility programs that are accessible through the Operating System.

Program Execution: Program execution needs instructions and data to be loaded in to main menu, Input / Output devices and files to be initialized and other resources to be prepared. The operating system handles all these tasks for the user.

Access to Input / Output devices: Each Input / Output device requires its own peculiar set of instructions of control signals for operation. Operating system takes care of details so, the programmes can think in terms of simple read and writes.

Controlled access to files: Operating system provides protection mechanisms to controlled access to files.

System Access: Operating System controls access to the system as a whole and to specific system resources.

Error detection and response: Variety of errors can occur which a computer system is running, i.e., internal and external hardware errors, such as memory error, device failure error, various software errors, inability of Operating System to grant request of an application errors and so on. In each case, Operating System must make the response that clears the error condition. The response may range from ending the program that caused the error, to retrying the operation to simply reporting the error to the application.

Accounting: A good Operating System collects usage statistics for various resources and monitors performance parameters such as response time, which can be used for billing purposes on a multi-user system.


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