CPU Scheduling Algorithms: FCFS, SJF, and Round Robin Quiz Quiz

Explore key concepts and differences among FCFS, SJF, and Round Robin CPU scheduling algorithms with this introductory quiz, designed to boost your understanding of process scheduling techniques, turnaround time, waiting time, and CPU burst prediction.

1. Basic Principle of FCFS

   Which core principle does the First-Come First-Served (FCFS) CPU scheduling algorithm follow?

   1. Processes are handled in the order of their arrival time.
   2. Priority is given based on the process number.
   3. The process with the shortest CPU burst executes next.
   4. Each process receives a fixed time interval (quantum).

   Explanation: FCFS selects processes based on the order they arrive, much like a queue. Unlike SJF, it does not consider CPU burst length. The fixed time quantum is used in Round Robin, not FCFS. Choosing by process number is unrelated to FCFS's actual working.

2. Shortest Job First Concept

   In the Shortest Job First (SJF) algorithm, how is the next process for execution chosen?

   1. By process priority set by the user.
   2. By selecting the process with the least CPU burst time.
   3. Randomly from the list of ready processes.
   4. Based on the highest process ID.

   Explanation: SJF works by picking the process that has the shortest estimated CPU burst next. This minimizes average waiting time. Process ID, user priority, or random selection are not the determining factors in SJF scheduling.

3. Preemption in Round Robin

   What occurs if a process does not finish within its allotted time quantum in Round Robin scheduling?

   1. It is sent to the end of the ready queue for another turn.
   2. Its priority is increased automatically.
   3. It continues running until it completes.
   4. It is terminated immediately.

   Explanation: In Round Robin, a process that exceeds its time slice is put at the queue's end to wait for another cycle. It is not terminated or allowed to run non-stop, and its priority does not automatically increase. This ensures fair CPU sharing among processes.

4. Context Switching Overhead

   Which CPU scheduling algorithm is most likely to result in a high overhead due to frequent context switches?

   1. Shortest Job First
   2. Priority Scheduling
   3. First-Come First-Served
   4. Round Robin

   Explanation: Round Robin can lead to frequent context switches due to its regular, short time slices allocated to each process. FCFS and SJF usually have fewer context switches since they allow longer uninterrupted runs. While Priority Scheduling can have some overhead, it is not typically as high as in Round Robin.

5. Turnaround Time in SJF

   Which scheduling method generally produces the lowest average turnaround time for a set of jobs with varying burst lengths?

   1. Shortest Job First
   2. Random Scheduling
   3. Round Robin
   4. First-Come First-Served

   Explanation: SJF tends to provide the minimum average turnaround time because shorter tasks are completed before longer ones, reducing the average wait. FCFS can lead to higher turnaround times due to possible convoy effects. Round Robin is designed for fairness rather than speed, and random scheduling does not optimize turnaround time.

6. Responding to a New Process

   If a new process arrives while the CPU is busy running another process under FCFS scheduling, what happens?

   1. The new process replaces the running process immediately.
   2. The CPU switches to the new process if its burst is shorter.
   3. The new process waits in the queue until the current process finishes.
   4. Both processes run simultaneously.

   Explanation: FCFS is non-preemptive, so the CPU completes the running process before starting the next one, regardless of the new process's burst time. It doesn't preempt or run multiple processes simultaneously. Resource allocation is strictly orderly.

7. Handling Long Processes in SJF

   What is a notable drawback of non-preemptive Shortest Job First (SJF) scheduling for processes with long CPU bursts?

   1. It only works for batch systems.
   2. All processes must have the same priority.
   3. Long processes may experience starvation and never get CPU time.
   4. Context switching is extremely high.

   Explanation: In non-preemptive SJF, long processes can be delayed indefinitely if shorter jobs keep arriving, leading to starvation. Priority sameness is unrelated to SJF. Context switching is not a primary issue in non-preemptive SJF. SJF can be used in other system types, not just batch systems.

8. Time Quantum in Round Robin

   What is the main effect of selecting a very large time quantum in the Round Robin CPU scheduling algorithm?

   1. Round Robin behaves similarly to FCFS scheduling.
   2. It eliminates the ready queue completely.
   3. It ensures shortest jobs always finish first.
   4. It minimizes all context switches.

   Explanation: A large time quantum allows each process to run until completion, effectively making Round Robin act like FCFS. Context switches are reduced, but not completely eliminated. Job order remains based on queue, not length, and the ready queue is still required for process management.

9. Predicting Next CPU Burst in SJF

   How does SJF usually estimate or predict the next CPU burst time for a process?

   1. By always using the same value for every process.
   2. By taking the maximum of all past bursts.
   3. By using exponential averaging based on the previous bursts.
   4. By assigning a random burst time.

   Explanation: SJF often predicts burst times using an exponential moving average of previous CPU bursts, which helps estimate the next value. Assigning burst times randomly, always choosing the maximum, or using a fixed value for all processes are not standard predictive methods.

10. Fairness in Scheduling

    Which CPU scheduling algorithm is specifically designed to ensure all processes get an equal share of CPU time in the short term?

    1. Round Robin
    2. Shortest Job First
    3. Priority Scheduling
    4. First-Come First-Served

    Explanation: Round Robin distributes CPU time slices evenly among all ready processes, maximizing fairness in the short term. Priority scheduling and SJF may favor certain jobs over others, while FCFS only provides fairness in terms of arrival order, not time-sharing.