Need and Services of Operating System

Operating System performs a number of functions for the computer system that are as follows:

It act as an extended machine
Operating system act as an extended machine by translating the commands, which are written in human understandable form into machine understandable instructions? After the execution of instruction by CPU it retranslates the Output back into a human understandable language.  Below figure show the extendable machine view of an operating system.

Extended Mchine view of Operating System

In this figure   N numbers of users are developing g and compiling their application program and are working in the text editor. All the users can interact with the operating system using system call or shell. To execute user’s job the operating system interact with Computer hardware.
It acts as a resource manager
An operating system act as resource managers. Operating system manages the resource in two ways:
•    Time Multiplexing
•    Space Multiplexing

In time multiplexing, different resources can be shared by controlling and allocating various hardware and software resources to different users in an optimal and efficient manner among different programs for a fix time of slots.

In space multiplexing, different resources are shared at the same time among different programs.  Example of space multiplexing includes sharing of a hard disk and main memory by different users at the same time.
It acts as a constant application program interface
The operating system is an interface that helps develop an application of a computer and executes the application on another computer. No variation is produce if the configuration of computer is different. For example, Windows 98 operating system has such kind of flexibility. It can hold different disk drivers, printers and peripherals, which are produce by different venders without any variation. Other functions of operating system are:
•    Control the device drivers attached to the computer.
•    Acts as a command interpreter.
•    Helps in determining the priority of jobs.
•    Enable you to perform the allocation and reallocation of memory.
•    Enables you to perform various input/output Operations
•    Provides security by ensuring controlled access to resource
•    Monitor various jobs, to ensure their security
•    Allow different process to communicate with each other through message passing techniques.
•    Enables you to perform system accounting that monitors the use of system resource.

Microsoft Windows Operating System

Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces (GUIs).[1] Microsoft Windows came to dominate the world’s personal computer market, overtaking Mac OS, which had been introduced previously. At the 2004 IDC Directions conference, it was stated that Windows had approximately 90% of the client operating system market.[2] The most recent client version of Windows is Windows Vista; the most recent server version is Windows Server 2008.

What is an Operating System

The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop — it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

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 DOS and UNIX, are not real-time.

Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.

As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.