Difference between Real-Time Operating System and Timesharing Operating System

Real-time Operating System

In a real time operating system (RTOS), a job is to be completed within the rigid time constraints otherwise job loses its meaning.
A real time system functions correctly only if it returns the correct result within its time constraints.
Thus, in a real-time system, the correctness of the computation not only depends upon the logical correctness of the computation but also upon the time at which the result is produced.
Thus, a real time system is one that must react to inputs and respond to them quickly. It cannot afford to be late with a response to an event.
A real time system is often used as a central device in a dedicated applications like fuel- injection system, robotics, air-traffic control, medical imaging systems, systems that control scientific experiment, industrial control system and weapon systems, traffic light system, radar system and telephone switching system.
Thus, providing quick response times is the main objective of real-time system, However, resource utilization and user convenience are of secondary concern.

Timesharing refers to the allocation of computer resources in a time dependent fashion to several programs simultaneously.
A timesharing system has many user terminals that are connected to same computer simultaneously. Using these terminal, different users can work on a system at the same time.
Thus, it uses multiprogramming with a special CPU scheduling algorithm to achieve this. In timesharing system, the CPU time is divided among all the users on a scheduled basis.
Each user program is allocated a very short period of CPU time one-by-one, beginning from the first user program and proceeding the last one, and then again beginning from the first one.
This short period of time during which user gets the attention of the CPU is known as a time slice, time slot or quantum. It is typically of the order of 10 to 100 milliseconds.
Thus, in timesharing, when the CPU is allocated to a user program, the user uses the CPU for the period of time slot.

It releases the CPU under any of the following three conditions :

S.No.	Real-Time Operating System	Timesharing Operating System
1.	A real time operating system has well defined fixed time constraints. Process must be done within the defined constraints or system will fail.	The time sharing system executes one job up to certain period of time and then switches to another job and so on.
2.	Certain operating system features like job scheduling, memory swapping have limited use.	Concepts like job scheduling, memory swapping are used for handling timesharing systems.
3.	It executes one job dedicatedly.	It seems to execute many jobs at the same time.
4.	Real time operating system enables us to program an application with predictable results.	It is impossible to predict response in advance in timesharing system.
5.	Real-time operating systems give users the ability to prioritize tasks so that the most critical task can always take control of the process when needed.	In timesharing system, high priority tasks can be preempted by lower priority tasks, making it impossible to guarantee a response time for your critical applications