RR (Round-Robin (a type of scheduler))

Round-Robin (RR) is a type of scheduling algorithm used in computer operating systems and job scheduling systems. It is designed to provide fairness and ensure that each process or task gets an equal share of the CPU time in a time-sliced manner. In RR scheduling, processes are assigned CPU time slices, known as time quantum or time slice, and they execute for the duration of their assigned time slice before being preempted and placed back into the scheduling queue.

Here's a detailed explanation of how Round-Robin scheduling works:

1. Time Quantum: The key concept in Round-Robin scheduling is the time quantum, which determines the maximum amount of CPU time a process can use in one round. The time quantum is a predefined value set by the system administrator or the operating system.
2. Ready Queue: The RR algorithm maintains a ready queue, which is a data structure that holds all the processes that are waiting to be executed. The ready queue is typically implemented as a FIFO (First-In-First-Out) queue.
3. Process Execution: When a process arrives or becomes ready for execution, it is added to the end of the ready queue. The scheduler then selects the process at the front of the queue for execution.
4. Time Slicing: The selected process is allocated the time quantum for execution. It starts executing and continues until it either completes its execution or its time quantum expires. If the process completes before the time quantum expires, it is removed from the ready queue.
5. Preemption: If a process's time quantum expires before it completes, it is preempted by the scheduler. The process is temporarily suspended, and its state is saved for later resumption. The process is then moved to the end of the ready queue, allowing the next process in the queue to execute.
6. Context Switching: When a process is preempted or completes its execution, a context switch occurs. The context switch involves saving the current process's state (such as register values, program counter, and other relevant data) and loading the state of the next process to be executed.
7. Scheduling Cycle: The above steps are repeated in a cyclic manner, creating a scheduling cycle. The scheduler continues to select processes from the front of the ready queue, allocating them the time quantum, and preempts them if necessary. This ensures that all processes get an equal opportunity to execute.
8. Fairness: Round-Robin scheduling provides fairness by giving each process an equal share of the CPU time. If multiple processes are in the ready queue, they are executed in a sequential manner based on their arrival time, and no process is starved of CPU time indefinitely.
9. Time Quantum Selection: The choice of an appropriate time quantum is crucial for achieving a balance between responsiveness and efficiency. A small time quantum provides more frequent context switches, ensuring better responsiveness but also introduces more overhead due to frequent context switches. A larger time quantum reduces the number of context switches but can lead to decreased responsiveness for interactive processes.

Round-Robin scheduling is commonly used in multi-user systems, time-sharing systems, and real-time operating systems. It provides a fair and predictable execution environment, ensuring that all processes receive a fair share of CPU time, preventing any single process from monopolizing system resources.