What is dispatcher and difference between dispatcher and scheduler?

The dispatcher is a crucial component of the operating system that works after the scheduler has made its decision. It gives control of the CPU to the process selected by the short-term scheduler by performing the actual context switching and transferring CPU control to the chosen process.

Functions of Dispatcher

The dispatcher performs several critical functions to transfer CPU control −

• Context switching − Saving the current process state and loading the selected process state.

• Switching to user mode − Changing from kernel mode to user mode for process execution.

• Jumping to the proper location − Setting the program counter to resume execution at the correct instruction.

• Dispatch latency − The time taken to stop one process and start another is called dispatch latency.

Difference Between Scheduler and Dispatcher

Role of Dispatcher in CPU Scheduling

The dispatcher plays a vital role in CPU scheduling by acting as the bridge between scheduling decisions and actual process execution. When the scheduler selects a process, the dispatcher must −

• Save the context of the currently running process (if any)

• Load the context of the newly selected process

• Switch from kernel mode to user mode

• Jump to the proper instruction in the user program

The dispatch latency is the time consumed by this entire switching process. Since dispatching occurs frequently in multitasking systems, minimizing dispatch latency is crucial for system performance. Modern operating systems optimize dispatcher code to reduce this overhead and improve overall system responsiveness.

Conclusion

The dispatcher is the execution component that works after the scheduler's decision-making process. While the scheduler determines which process should run next, the dispatcher actually performs the context switch to make it happen. Together, they enable efficient CPU scheduling and multitasking in modern operating systems.