What is Operating system ?

Operating system (OS) is a software program that control the internal activities of the computer hardware and provides user interface.Application programs need to interact with the operating system for using hardware resources.

OS is the first program loaded (copied) into the computer's main memory after the computer is switched on.

The operating system is primarily concerned with allocating and de-allocating computer resources to one or more jobs.

The main functions of an operating system are :

• Resource Management (Processor Management, Memory Management, Device Management)
• Process Management (Job scheduling, Task Management)
• Data Management (File Management and Input/Output Management)
• Security management

All operating system can be classified into four categories :

• Single User Operating System:Operating system which allows only one user to work on a computer at a time is known as single user operating system. Examples:DOS,Windows,etc.
• Multi-user Operating system: A multi-user operating system allows a number of users to work together on a single computer. Each user will be provided a terminal connected to a computer. Example : Linux, UNIX, Windows 2000,etc.
• Single Tasking Operating System: Operating system which can execute only a single task at a time is known as single tasking operating system. Example: DOS
• Multi-tasking Operating system: Multi-tasking operating system supports execution of more than one job at a time. Most of today"s operating systems such as Windows 2000, OS/2,UNIX, Linux, etc. support multi tasking. 

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In sort form :

Operating system is to provide an interface between the user and the hardware. this interface enables a user hardware resources efficiently.The main functions of operating system are 

1. Resource management  
2. Process management 
3. Data management 
4. Security management.

It's classified into four categories

1. Single User Operating system
2. Multi-user Operating system
3. Single Tasking Operating System
4. Multi-tasking Operating system

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• Differences between system and application software