What is Scheduling in Operating System?

Scheduling in an operating system refers to the process of determining the order in which tasks or processes are executed by the CPU. The primary goal of scheduling is to make the best use of system resources, especially the CPU, to ensure efficient and fair execution of processes. The scheduling algorithm is responsible for selecting the next process to run from the ready queue.

Key Concepts:

Process State:

• New: The process is being created.
• Ready: The process is waiting to be assigned to a processor.
• Running: The process is currently being executed.
• Blocked (or Waiting): The process is waiting for some event to occur.
• Terminated (or Completed): The process has finished execution.

Scheduling Queues:

• Ready Queue: Processes that are ready to be executed but are waiting for the CPU.
• Blocked Queue: Processes that are waiting for some event, such as I/O, to occur.

Scheduling Criteria:

• CPU Utilization: Maximizing CPU usage to keep it busy.
• Throughput: The number of processes completed in a given time.
• Turnaround Time: The total time taken to execute a process, including waiting and execution time.
• Waiting Time: The total time a process spends waiting in the ready queue.
• Response Time: The time it takes for the system to respond to a user's input.

Scheduling Algorithms:

• First-Come, First-Served (FCFS): Processes are executed in the order they arrive.
• Shortest Job Next (SJN) or Shortest Job First (SJF): The process with the shortest burst time is executed first.
• Priority Scheduling: Each process is assigned a priority, and the process with the highest priority is executed first.
• Round Robin (RR): Each process is assigned a fixed time slice (time quantum) before moving to the next process in the queue.

Preemptive vs. Non-Preemptive Scheduling:

• Preemptive: The operating system can interrupt a running process and start or resume another.
• Non-Preemptive: Once a process starts its execution, it continues until completion without interruption.

Objectives of Scheduling:

• Fairness: Ensuring each process gets a fair share of CPU time.
• Efficiency: Maximizing CPU utilization and throughput.
• Minimization of Waiting Time: Reducing the time processes spend waiting in the ready queue.
• Minimization of Turnaround Time: Reducing the overall time taken for a process to complete.

Scheduling plays a crucial role in achieving efficient resource utilization and maintaining a responsive and fair operating system environment. The choice of scheduling algorithm depends on the characteristics of the system, the workload, and the desired performance metrics.

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