Time Sharing Operating System

It refers to allocation of computer resources in time dependent fashion to several user simultaneously. It provides a large number of users with direct access to computer for solving their problems. 

In this kind of system a separate terminal of system is provided for each user. All these terminals are connected to the main computer system. In time sharing system the CPU time is divided along all user and a fixed time is allowed to each user. The programming speed of the system allows the CPU to switch from one user to another user at a very fast speed giving an illusion to each user that only his program is running. 
Time  sharing system is also known as "Round Robin Method".

In this system only one program can be in control of the CPU at a given instance so all the programs will fall in one of the following stages:

ACTIVE STAGE

User’s program has got control on the CPU. Only one  program can be active at given instruction of time.

READY STAGE

User’s program is ready to execute but it is waiting for its turn to get the CPU time.

WAITING STAGE

User has made no requirement for execution of his program and is waiting for completion of same input/output operations.