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Operating System (OS) is a computer program (System Software) that acts as an intermediate between the user and computer hardware. This is the first software we see when we turn on the computer and again the last software we see when the computer is turned off. It is very difficult for the users of computer to understand how to operate them directly. So, OS becomes the interpreter between the computer hardware and user. It interprets the command of users to the hardware and presents the output to user in a suitable format produced by hardware.
Types of Operating System
There are 7 types of operating system which are given bellow:
- Batch System : A batch system is one which jobs are bundled together with the instruction necessary to allow them to be processed without user intervention. The simple Operating System also called monitor is system software responsible for interpreting and carrying out the instructions in the batch jobs. When the monitor started a job, it handed over control of the entire computer to the job, which then controls the computer until it is finished. Such batch system is called Stacked Job or simple batch system.
- Multiprogramming System : As computes started having more and more memory, it was possible to extend the idea of multiprogramming. The concept of multiprogramming is to create systems that would load several jobs into memory at once and cycle through them in some order, working on each one for a specified period of time.
- Timesharing System : Time Sharing System designed to enable many users to interact with the computer system at the same time by using a terminal keyboard and display device. This strategy was the first step in making the computer available to many people involved in many different types of information processing task. The Time Sharing System focus on policies to implement equitable processor sharing. This allows users to treat the machine as if they have exclusive control of a "comparatively slow" computer the virtual machine.
- Real Time Operating System : Real Time Operating System are dedicated to some well-defined jobs which require vary fast response time. The system must be fault-tolerant that is OS must handle the error without going to unstable stage. The execution time is most critical issue in real time OS and they must finish the execution of job within pre-defined time-boundary. The example of programs that run in Real-Time OS are: missile guiding system, medical monitoring system, flight simulation system etc. To finish the job after the dead line is as worse as not performing the job.
- Multi-Processing Operating System : A Multiprocessing Operating System is one which runs on the computer having more than one CPU. Such OS simultaneously execute two or more jobs at a single time. Since all the other previously defined OS contains only one processor, the controlling mechanism in Multiprocessing OS becomes a bit complex. Nowadays, multi processing is performed even by a single processer system. Different jobs get the single CPU at faster rate giving illusion to user called as pseudo-parallelism. In windows, we can type in word processor, listen to music, download file and so forth simultaneously even though there is a single CPU. There is a fast switching of different jobs, so we feel as if different programs are running at the same time.
- Network Operating System : Most of the Network OS works under the principle of Client server mechanism. Client Server is a mechanism in which co-operation and intercommunication between various elements of network takes place and more machine "serves" other for various functions. The users are aware of the existence of multiple computers and can use the functionality of remote machines. In other words, a user doesn't have to sit in front of machine in which he wants to work on.
- Distributed Operating System : A Distributed OS is one that appears to its user as a traditionally uni-processor system, even though it is actually composed of multiple processors/ computers. The user mustn't be aware of where there application/ program is running or where there file is located. The user feels like he is working in the terminal in front of him, but actually the work many may take place in any machine in the network. It is the job of operating system to create such transparency.
Function of Operating system
OS is an interface between user and the hardware, so it take the entire burden form user for managing various resource of computer system. Moreover, co-ordination between the resources, reliability and efficiency are also the key terms OS is directly connected with. In the general, OS does the following core functions.
- Security : One of the major tasks of OS is to secure the data and program space of each job while loaded into the memory. One program isn't allowed to capture the program or data space of the program, for that OS maintains the boundary of each job in the memory and each job are allowed to run only in that boundary. In multi user system, the OS must manage security measures to prevent data of one user by other.
- File Management : Operating System handles the file organizations in the secondary storage devices. Following measures are taken by OS for file management.
- Maintains a mechanism of files and directories, where files can be kept in separate directories in an organized manner.
- Creates a table of each files and directories in the storage device. For example FAT in DOS, NTFS in Windows, and ext3 in Linux. They keep track of each element efficiently.
- Maintains authority over files by allowing different types of access permission and priority.
- Implements different types of efficient searching mechanism of files.
- Device Drivers : Device Drivers are important for a computer system to work properly. Without a device driver, the particular hardware fails to work accordingly, which means it fails in doing a particular action for which it has been created.
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