Non-preemptive Scheduling in Operating Systems
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Questions and Answers

What is a notable disadvantage of using First Come First Serve (FCFS) scheduling?

  • It can lead to a convoy effect. (correct)
  • It allows preemption of currently running processes.
  • It ensures fairness among processes.
  • Processes are executed in the order they arrive.

    • What is the primary objective of maximizing CPU utilization in scheduling algorithms?

  • To reduce the turnaround time for individual processes.
  • To keep the CPU as busy as possible. (correct)
  • To minimize the response time for processes.
  • To ensure all processes get equal time on the CPU.

    • How is turnaround time calculated?

  • Completion Time + Arrival Time
  • Turnaround Time + Waiting Time
  • Completion Time - Burst Time
  • Completion Time - Arrival Time (correct)

    • Which of the following scheduling criteria focuses on the responsiveness of the system?

    <p>Response Time</p> Signup and view all the answers

    In what situation does a non-preemptive scheduling algorithm present challenges?

    <p>When short processes must wait for a long process to complete.</p> Signup and view all the answers

    What is the key function of throughput in scheduling algorithms?

    <p>To measure the rate of process completion.</p> Signup and view all the answers

    Which characteristic distinguishes non-preemptive scheduling from preemptive scheduling?

    <p>Once a process is running, it cannot be interrupted.</p> Signup and view all the answers

    What does fairness in scheduling aim to achieve?

    <p>To ensure each process receives CPU time periodically.</p> Signup and view all the answers

    What scheduling algorithm does the provided data primarily illustrate?

    <p>Shortest Job First</p> Signup and view all the answers

    Which process has the highest turnaround time in the given data?

    <p>P1</p> Signup and view all the answers

    In the context of non-preemptive priority scheduling, what happens when a new process with a higher priority arrives?

    <p>The currently running process continues until it completes.</p> Signup and view all the answers

    Which of the following accurately describes the SJF scheduling algorithm?

    <p>It selects the process with the shortest burst time next.</p> Signup and view all the answers

    In which scenario would preemptive priority scheduling be advantageous?

    <p>When maximizing the response time of the highest priority process.</p> Signup and view all the answers

    How is the priority determined in a priority scheduling algorithm?

    <p>By an integer associated with each process, where a smaller integer represents higher priority.</p> Signup and view all the answers

    Which of the following statements about preemptive scheduling is true?

    <p>It allows a higher priority process to take over the CPU immediately.</p> Signup and view all the answers

    What is one benefit of non-preemptive priority scheduling compared to the preemptive version?

    <p>It reduces the overhead caused by context switching.</p> Signup and view all the answers

    What is the average waiting time for the processes P1, P2, and P3 when they arrive in the order P1, P2, P3?

    <p>17 milliseconds</p> Signup and view all the answers

    When the processes arrive in the order P2, P3, P1, what is the average waiting time calculated?

    <p>3 milliseconds</p> Signup and view all the answers

    In the scenario with processes P1, P2, P3, what is the completion time for process P3 when they arrive in the order P1, P2, P3?

    <p>30</p> Signup and view all the answers

    Which of the following formulas is used to calculate the waiting time for a process?

    <p>Turnaround Time - Burst Time</p> Signup and view all the answers

    What is the average turnaround time for the processes given with burst times of P1=21, P2=3, P3=6, and P4=2?

    <p>26.75 milliseconds</p> Signup and view all the answers

    If the arrival times for processes P1, P2, P3, P4, and P5 are 0, 1, 2, 3, and 4 respectively, what is the waiting time for P4?

    <p>5 milliseconds</p> Signup and view all the answers

    What is the turnaround time for process P2 with a burst time of 3 and an arrival time of 1?

    <p>4 milliseconds</p> Signup and view all the answers

    When processes come in the order P1, P2, P3, what is the waiting time for process P2?

    <p>24 milliseconds</p> Signup and view all the answers

    What is the average completion time for three processes with burst times of P1 = 24, P2 = 3, and P3 = 3 when ordered as P1, P2, P3?

    <p>27 milliseconds</p> Signup and view all the answers

    What is a potential disadvantage of non-preemptive priority scheduling?

    <p>Starvation may occur for lower priority processes</p> Signup and view all the answers

    In the example provided, which process has the highest priority?

    <p>P1</p> Signup and view all the answers

    What does Round Robin scheduling primarily utilize to manage processes?

    <p>A fixed time quantum for execution</p> Signup and view all the answers

    Which process has the shortest turnaround time in the examples provided?

    <p>P1</p> Signup and view all the answers

    In preemptive priority scheduling, when can a process be interrupted?

    <p>Whenever a higher priority process arrives</p> Signup and view all the answers

    From the provided data, which process experiences the highest waiting time?

    <p>P2</p> Signup and view all the answers

    What is the impact of burst time on completion time for a process?

    <p>Longer burst time can delay completion time</p> Signup and view all the answers

    What characterizes a preemptive scheduling algorithm?

    <p>Processes may be interrupted to allow higher priority tasks to run</p> Signup and view all the answers

    What is the purpose of context switching in a preemptive scheduling system?

    <p>To save the state of preempted processes</p> Signup and view all the answers

    In round robin scheduling, what does 'time quantum' refer to?

    <p>The fixed time each process is allowed to run before being preempted</p> Signup and view all the answers

    What characterizes multilevel queue scheduling?

    <p>The ready queue is divided into permanent, separate queues</p> Signup and view all the answers

    What is the main advantage of the round robin scheduling algorithm?

    <p>It allows processes to share CPU time more fairly</p> Signup and view all the answers

    How is the waiting time for a process calculated in scheduling?

    <p>Completion time minus burst time and arrival time</p> Signup and view all the answers

    Which of the following is NOT a characteristic feature of round robin scheduling?

    <p>It can lead to starvation of processes</p> Signup and view all the answers

    Study Notes

    Non-preemptive Scheduling

    • Non-preemptive algorithms prevent processes from being interrupted once in the running state until they complete their time allocation.

    Scheduling Criteria

    • CPU Utilization: The goal is to keep the CPU active, ideally between 40-90% for optimal performance.
    • Throughput: Measures how many processes are completed in a certain time frame.
    • Turnaround Time: Total time taken for process execution, calculated as Completion Time - Arrival Time.
    • Waiting Time: Total time spent in the ready queue, found by subtracting burst time from turnaround time.
    • Response Time: Duration from submission of a request until the first response is received.
    • Fairness: Ensures equal CPU sharing among processes.

    Scheduling Algorithm Optimization Criteria

    • Maximize CPU utilization
    • Maximize throughput
    • Minimize turnaround time
    • Minimize waiting time
    • Minimize response time

    Types of Scheduling Algorithms

    • First Come First Serve (FCFS)
    • Shortest Job First (SJF)
    • Priority Scheduling
    • Round Robin (RR) Scheduling
    • Multilevel Queue Scheduling
    • Multilevel Feedback Queue Scheduling

    First Come First Serve (FCFS) Scheduling

    • Processes are executed in the order they arrive.
    • Simple to implement but can lead to high average wait times, especially in time-sharing systems.
    • Disadvantage: Convoy effect occurs when short processes wait for a long process, reducing CPU utilization.

    FCFS Example

    • When processes P1 (24), P2 (3), and P3 (3) arrive in order:
      • Gantt Chart: P1 (0-24), P2 (24-27), P3 (27-30)
      • Waiting Time: P1 = 0, P2 = 24, P3 = 27; Average = 17 ms
    • If they arrive as P2, P3, P1:
      • Gantt Chart: P2 (0-3), P3 (3-6), P1 (6-30)
      • Waiting Time: P1 = 6, P2 = 0, P3 = 3; Average = 3 ms

    Shortest Job First (SJF)

    • Selects processes with the least execution time first.
    • Can be both non-preemptive and preemptive.

    Priority Scheduling

    • Assigns a priority to each process, highest priority gets CPU first.
    • Can lead to starvation for low-priority processes.
    • Can be either preemptive or non-preemptive.

    Round Robin (RR) Scheduling

    • A preemptive scheduling algorithm where each process runs for a set time slice (quantum) before being preempted.
    • Context switching saves states of preempted processes.

    Multilevel Queue Scheduling

    • A strategy that separates processes into distinct queues based on task type, with each queue having different scheduling priorities.
    • Processes are permanently assigned to a specific queue.

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    Related Documents

    Unit2_CPU Scheduling.pptx

    Description

    Explore the principles of non-preemptive scheduling algorithms and their impact on CPU utilization, turnaround time, and fairness. This quiz covers the criteria for scheduling performance and the optimization goals in operating systems. Test your understanding of non-preemptive scheduling methods and their significance.

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