Difference Between Scheduler and Dispatcher
Difference between Scheduler & Dispatcher
Difference Between Scheduler and Dispatcher refers to the distinction between two key components of an operating system’s process management. On this page, we will learn the concepts of scheduler and dispatcher and also compare the differences between the two. These components are essential in CPU scheduling and help manage process execution efficiently.
On this page, we will learn the concepts of scheduler and dispatcher and also compare the differences between the two.
Schedulers selects a process out of the several processes that need to be executed.
Dispatcher performs the function of switching contexts, switching to user mode and many other.
Scheduler
Schedulers are system software that handle the removal of the running process from the CPU and the selection of another process. It selects a process out of several processes that need to be executed.
There are three types of schedulers in an operating system.
1. Long Term Scheduler
It is also known as a job. It decides the degree of multi programming of the system. In simple words, when multiple processes are waiting for the execution, processes having small size are placed in the secondary storage. Then long term scheduler selects the processes from the job queue and brings that process to the ready queue in the main memory.
2. Medium-Term Scheduler
A running process needs input/output operations. The process goes to waiting state when not in need. This process is called suspended. However, CPU is used to its full utilization, while running the other process. Meanwhile, the suspended process is transferred back to the secondary memory. Now, the transferred process can return back to the main memory and continue its execution.
This transfer of suspended process to the secondary memory is called swapping out and bringing the process back to the main memory is known as swapping in. It removes processes from memory, and thus, reduces the degree of multi-programming.
3. Short Term Scheduler
It is also known as CPU scheduler. It selects a process in the ready queue that should be allocated for execution. When it picks the process from the ready queue, the previous task goes to the waiting state. This process is completed in a fraction of seconds to avoid wasting the CPU time.
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Dispatcher
The dispatcher is a component of the operating system responsible for transferring control of the CPU to the process selected by the short-term scheduler. It performs the context switch, enabling multitasking by switching between processes or threads.
Key Responsibilities of the Dispatcher:
- Context Switching
Saves the state (registers, program counter, etc.) of the currently running process and restores the state of the new process. - Switching to User Mode
Switches the CPU mode from kernel mode to user mode so the process can run safely without full system privileges. - Jumping to the Proper Location
Transfers control to the instruction where the selected process last left off.
Difference between Scheduler and Dispatcher
| Feature | Scheduler | Dispatcher |
|---|---|---|
| Function | Selects which process to run next | Gives control of the CPU to the selected process |
| Role | Decision-maker for process selection | Executor of that decision |
| Timing | Runs before the process is chosen | Runs after the scheduler chooses a process |
| Involves | Algorithm-based selection (e.g., FCFS, Round Robin) | Context switching, mode switching, jumping to user code |
| Speed Impact | Affects overall system scheduling efficiency | Affects the speed of context switching (dispatch latency) |
Final Thoughts
Both the scheduler and dispatcher are vital components of an operating system’s process management. The scheduler is responsible for selecting which process should run next, using various scheduling algorithms. On the other hand, the dispatcher executes this decision by performing tasks like context switching and transferring control to the selected process. While the scheduler focuses on decision-making, the dispatcher ensures smooth execution. Together, they manage CPU utilization efficiently and enable multitasking. Understanding their roles helps in grasping the inner workings of modern operating systems.
FAQs
If the dispatcher fails, the system may crash or freeze, as it cannot properly switch between processes.
Yes, but it may result in inefficient CPU usage and memory overload due to uncontrolled process inflow.
Yes, high dispatcher latency can delay process execution and reduce overall system responsiveness.
Yes, all modern operating systems use them, though their implementation may vary across systems.
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