Operating System is a software program that acts as an interface between the user and the computer. It is a software package which allows the computer to function.

The two main functions of an operating system are:

To manage the hardware resources of a computer To provide the applications with a easy way to use the hardware

resources of the computer without the applications having to know all of those details. This, in computing jargon is called being a Application programming interface (API)

One of the challenges facing developers is keeping their operating systems flexible enough to run hardware from the thousands of vendors manufacturing computer equipment. Today's systems can accommodate thousands of different printers, disk drives and special peripherals in any possible combination

   The main functions of an Operating systems are

Processor management

Memory management,

Storage management and

Device management 

      all of the above coming under hardware managing capabilities of an operating system, while the following come under software capabilities of an operating system.

Application interface

         Application programming interface is that where the operating system creates link between the application and system providing an active link between the program and hardware of the computer.

User interface

     User interface provides  a link between the user and the computer, which is one of the main functions of an OS. This can be from providing user with the convenience of giving text commands or else giving the comfort of playing something with the graphics that are built in the operating system to get the desired results. Keeping in mind, a User who doesn't want to be a  professional to be able to operate a computer,

graphic user interfaced Operating systems are more popular in the market and even the free source Linux is also being available in graphic user

Functions:

1. Program creation2. Program execution3. Access to Input/output devices4. Controlled access to files5. System access6. Error detection and response7. Interpreting the commands8. Managing peripherals9. Memory management10. Processor management11. Information management12. Process communication13. Netoworking

• Machine and Peripheral Management• Security• File Management• Device Drivers• Ability to Customize• Support for Connectivity of Portable Media• Security• Stability and Reliability• Ease of Management• Associated Utilities

14. • Machine and Peripheral Management• Security• File Management• Device Drivers

15. 1.Program execution2.I/O management3.CPU scheduling4.Error detection5.Accounting6.protection and security

1) to interprate the commands executed by the user.2) to handle disk input/output settings.3) loaded in the memory at bootup and remain in the memory at all time.

4) to provid the OS with the machanism in order to see the additional memory.5) used to access the high memory area. (himem.sys )6) it allows the rest of the OS and its programs to interact directry with the system hardware and the system BIOS.7) it sets particular values corresponding to the windows environment.8) used to run particular programs during startup.

2) functions==1 Recording input from the keyboard2 Display out put on the screen3 Manage files and directories in computer4 control the peripherals such as hdd, printer etc5 Other application programs(softwares) are run

Types of Operating System

DOS (Disk Operating System) UNIX LINUX Windows Windows NT

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.

real time: Responds to input instantly. General-purpose operating systems, such as

.

There are different types of operating systems. These are as follows:

1. Real-time Operating System: It is a multitasking operating system that aims at executing real-time applications.

2. Multi-user and Single-user Operating Systems: The operating systems of this type allow a multiple users to access a computer system concurrently.

3. Multi-tasking and Single-tasking Operating Systems:When a single program is allowed to run at a time, the system is grouped under a single-tasking system, while in case the operating system allows the execution of multiple tasks at one time, it is classified as a multi-tasking operating system.

4. Distributed Operating System: An operating system that manages a group of independent computers and makes them appear to be a single computer is known as a distributed operating system.

5. Embedded System: The operating systems designed for being used in embedded computer systems are known as embedded operating systems.

1. Operating Systems for Real-time OS: These types of OS are used to control machinery, control systems and industrial systems and have very less or in certain case no user-interface capability.

2. Operating Systems for Single User, Single Task OS: This is a typical computer system where one user can work effectively only on one task. Cell phones and palm tops are examples where these types of systems are used.

3. Operating Systems for Single User, Multi-tasking: Computer Operating Systems of desktops or laptops typically fall within this category. Here, the user can use several applications at a time.

4. Operating Systems for Multi-User: Here, various users use the computer system through different terminal and the Operating Systems on that computer has to balance multiple users with multiple applications.

Features• Ability to Customize• Support for Connectivity of Portable Media• Security• Stability and Reliability• Ease of Management• Associated Utilities

Different operating systems have differing features, though they all have the primary function of controlling the software and programs running on a computer or other device.

Popular features include:

A start menu or application menu (Windows, Linux)

Multiple desktop workspaces (Linux, Mac OS X)

Taskbar (Windows, Linux) or dock (Mac OS X, also Linux) to track favorite program shortcuts and active applications

A desktop environment. Linux has GNOME or KDE (and a few others), Mac has Aqua, and Windows Vista has Aero.

Desktop acceleration (Mac OS X, Linux using Compiz or similar, and Windows Vista Premium, Business, or Ultimate