classification of operating System

 Types of Operating System:

There are many different Operating Systems. But operating systems are mainly classified in several categories. These are the following –

1)      Single user and single tasking operating system 

2)      Single user and multitasking operating system

3)      Multiuser multitasking Operating System

 

1) Single user single tasking operating system: This operating system is very popular on personal computers. In this system one user works on a machine at a time. One program can be executed at a time. So this operating system is known as ‘Single user operating system’. If you have a large number of jobs to be executed on such a system, then you have to execute them one after another in sequence.

For example: Input and output devices like the printer are very slow as compared to the speed of a CPU. When, you give the printing command a CPU reads a file containing data and sends it to the printer. As the speed of the printer is very slow the CPU has to remain in state in idle state most at the time during printing. So the CPU is idle, you cannot run any program till printing is over , because the operating system is single tasking.  For example: MS-DOS (Microsoft Disk Operating System).

2) Single user multitasking operating system: This operating system has the ability to handle many programs at a one time, which all of them at different states of execution, that is known as multitasking. The main advantage of multiprogramming system is that user do not have to wait until the system finishes the execution of previously running program. User can execute the second program before the finish of the first one. In a multiprogramming system a number of program may be running concurrently.

For example- Suppose two program are running simultaneously on the computer at one stage, the first program start printing report on the printer. The printer is very slow therefore the CPU shifts its attention from the first program and pays more time executing the second program. Thus, the CPU does not remain idle on the other hand in the single tasking operating system, the CPU would remain idle whenever a programs starts any slow input/output operations. For example- Microsoft XP, Vista 7, 8 etc.

 

3) Multiuser multitasking Operating System: Multi-user operating system allows the concurrent access to many users of a computer. A multiuser operating system perform all the functions performed by single user system. That is memory management, input or output management, process management, information management, loading, linking and scheduling the resources etc. It has prevented problems, which can occur when two users are typing to access to the same file and to update at the same time.

            The multiuser operating system uses the time sharing technique. Therefore it is also known as time sharing operating system. The time shared operating system allows many users to simultaneously share the CPU time. A time shared operating system uses CPU scheduling and multiprogramming to provide computer time to each user. To explain how time sharing is done, let us consider as example 4 users are working on one computer having multiuser operating system. In this case 4 monitors and 4 keyboard and mouse are present. Through 4 cables these terminals are connected to a single CPU time is divided in to four parts. In short, it means that for the 1^st user CPU work only for the first few neon-second and then others the store the statues of the first user program and switches to the second user and does its job for the next few neon-seconds. As the second user finishes its status is also stored and CPU executes the program of the 3th user for next few neon-second and moves towards the fourth users. Again the CPU comes that to the first user and reads its status and works. Thus CPU works in cycles and works for more than one users.