Time Sharing Operating System

Time Sharing Operating System:

A time sharing system allows many users to share the computer resources simultaneously. In other words, time sharing refers to the allocation of computer resources in time slots to several programs simultaneously. For example- a mainframe computer that has many users logged on to it. Each user uses the resources of the mainframe that is memory, Microprocessor etc.

The time sharing systems are developed to provide an interactive use of the computer system. A time shared system uses CPU scheduling and multi-programming to provide each user with a small portion of a time shared computer. It allows many users to share the computer resources simultaneously. As the system switches rapidly from one user to the other user, a short time slot is given to each user for their executions program.The time sharing system provides the direct access to a large number of users where CPU time is divided among all the users on scheduled basis. The operating system allocates a set of time to each user. When this time is expired, it passes control to the next user on the system. This short period of time during that a user gets attention of the CPU that is known as a time slice. 


 







Figure: Time Sharing Operating System

In above diagram the user 6 is active but user 1, user 2, user 3, user 4 and user 5 are in waiting state whereas user 1 is in ready status. As soon as the time slice of user 6 is completed, the control moves on to the next ready user that is user 1. In this state user 2, user 3, user 4, and user 5 are in waiting state and user 1 is in ready state. The process continues in the same way and so on.

The time shared systems are more complex than the multi-programming systems. In time-shared systems multiple processes are managed simultaneously which requires an enough management of main memory so that the processes can be swapped in or swapped out within a short period of time.


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