Round Robin scheduling in Operating Systems - Mini Project: Build & Apply

Round Robin Scheduling Simulation

📖 Scenario: You are managing a simple computer system that runs multiple tasks. To be fair, the system uses Round Robin scheduling, which gives each task a small fixed time to run before moving to the next task.This helps all tasks get a chance to run without waiting too long.

🎯 Goal: Build a step-by-step simulation of Round Robin scheduling that shows how tasks are given time slices in order.

📋 What You'll Learn

Create a list of tasks with their required CPU times

Set a fixed time slice (quantum) for each task

Simulate the Round Robin scheduling by reducing task times in order

Show the order in which tasks get CPU time until all are done

💡 Why This Matters

🌍 Real World

Round Robin scheduling is used in operating systems to share CPU time fairly among multiple running programs.

💼 Career

Understanding Round Robin helps in roles like system administration, software development, and IT support where managing multitasking and performance is important.

1

Create the list of tasks with CPU times

Create a list called tasks with these exact tuples representing task names and their CPU times: ("Task1", 10), ("Task2", 4), ("Task3", 6).

Operating Systems

# Create the list of tasks with their CPU times
# Your code here

Hint

Use a list of tuples where each tuple has the task name as a string and its CPU time as an integer.

2

Set the time slice (quantum) for each task

Create a variable called time_slice and set it to the integer 3 to represent the fixed time each task gets to run before switching.

Operating Systems

tasks = [("Task1", 10), ("Task2", 4), ("Task3", 6)]
# Set the time slice for each task
# Your code here

Hint

The time slice is how many units of time each task runs before switching.

3

Simulate Round Robin scheduling to reduce task times

Create a new list called remaining_times that copies the CPU times from tasks. Then write a while loop that continues as long as any task has remaining time greater than zero. Inside the loop, use a for loop with variables index and (name, time) iterating over enumerate(tasks). For each task, if its remaining time is greater than zero, reduce it by time_slice but not below zero.

Operating Systems

tasks = [("Task1", 10), ("Task2", 4), ("Task3", 6)]
time_slice = 3
# Simulate Round Robin scheduling
# Your code here

Hint

Use a list to track remaining times and loops to reduce them by the time slice until all are zero.

4

Track and show the order of task execution

Inside the for loop from Step 3, add a list called execution_order before the while loop starts. Each time a task runs (when its remaining time is greater than zero), append its name from tasks[index][0] to execution_order. This list will show the order tasks got CPU time slices.

Operating Systems

tasks = [("Task1", 10), ("Task2", 4), ("Task3", 6)]
time_slice = 3
remaining_times = [time for _, time in tasks]
execution_order = []

while any(time > 0 for time in remaining_times):
    for index, (name, _) in enumerate(tasks):
        if remaining_times[index] > 0:
            # Append the task name to execution_order
            # Your code here
            remaining_times[index] = max(0, remaining_times[index] - time_slice)

Hint

Keep a list of task names in the order they get CPU time slices.

Practice

1. What is the main idea behind Round Robin scheduling in operating systems?

easy

A. The shortest job runs first until completion.

B. Processes are run based on their priority levels.

C. Each process gets an equal fixed time slice to run in turns.

D. Processes run only when they request CPU time.

Solution

1. Step 1: Understand Round Robin scheduling basics

   Round Robin scheduling assigns each process a fixed time slice called a quantum, and processes run in a cyclic order.

2. Step 2: Compare options with the definition

   Only "Each process gets an equal fixed time slice to run in turns." correctly describes this fixed time slice and cyclic turn-taking approach.

3. Final Answer:

   Each process gets an equal fixed time slice to run in turns. -> Option C

4. Quick Check:

   Round Robin = fixed time slice per process [OK]

Hint: Round Robin means equal time slices in a cycle [OK]

Common Mistakes:

• Confusing Round Robin with priority scheduling
• Thinking shortest job runs first
• Assuming processes run only on request

2. Which of the following is the correct way to represent the time quantum in Round Robin scheduling?

easy

A. A fixed time interval each process runs before switching.

B. The total time a process needs to complete.

C. The priority level assigned to a process.

D. The time a process waits before starting.

Solution

1. Step 1: Define time quantum in Round Robin

   The time quantum is the fixed time interval given to each process to run before the CPU switches to the next process.

2. Step 2: Eliminate incorrect options

   Options B, C, and D describe other concepts like total burst time, priority, and waiting time, not the time quantum.

3. Final Answer:

   A fixed time interval each process runs before switching. -> Option A

4. Quick Check:

   Time quantum = fixed run time per process [OK]

Hint: Time quantum is the fixed run time slice [OK]

Common Mistakes:

• Mixing time quantum with total process time
• Confusing quantum with priority
• Thinking quantum is waiting time

3. Consider three processes P1, P2, and P3 with burst times 5, 3, and 8 units respectively. Using Round Robin scheduling with a time quantum of 3 units, what is the order of process execution in the first two cycles?

medium

A. P1, P3, P2, P1, P2, P3

B. P3, P1, P2, P3, P1, P2

C. P2, P1, P3, P2, P1, P3

D. P1, P2, P3, P1, P3, P3

Solution

1. Step 1: Calculate first cycle execution

   Each process runs for 3 units or less if burst time is less. P1 runs 3 (remaining 2), P2 runs 3 (done), P3 runs 3 (remaining 5).

2. Step 2: Calculate second cycle execution

   Next, P1 runs remaining 2 (done), P3 runs 3 (remaining 2), then P3 runs remaining 2 (done).

3. Final Answer:

   P1, P2, P3, P1, P3, P3 -> Option D

4. Quick Check:

   Round Robin cycles through processes with quantum 3 [OK]

Hint: Run each process max quantum, repeat until done [OK]

Common Mistakes:

• Not updating remaining burst times correctly
• Mixing process order in cycles
• Assuming processes finish in one quantum

4. A Round Robin scheduler has a time quantum of 4 units. A process with burst time 6 units is scheduled. The process runs for 6 units without interruption. What is the likely error in the scheduling?

medium

A. The process voluntarily gave up CPU before quantum ended.

B. The time quantum was ignored; process should have been preempted after 4 units.

C. The scheduler used priority instead of Round Robin.

D. The process was too short to be preempted.

Solution

1. Step 1: Understand expected Round Robin behavior

   With quantum 4, a process running longer than 4 units should be preempted after 4 units to allow others to run.

2. Step 2: Analyze the given scenario

   The process ran full 6 units without interruption, which means the scheduler did not preempt it as expected.

3. Final Answer:

   The time quantum was ignored; process should have been preempted after 4 units. -> Option B

4. Quick Check:

   Quantum ignored means no preemption [OK]

Hint: Process must be preempted after quantum expires [OK]

Common Mistakes:

• Assuming short processes don't get preempted
• Confusing voluntary yield with scheduler preemption
• Ignoring time quantum enforcement

5. In a Round Robin system, if the time quantum is set too large, what is the most likely effect on system performance?

hard

A. It behaves like First-Come-First-Served, causing longer wait times for some processes.

B. Processes switch too frequently, increasing overhead.

C. All processes finish faster due to longer CPU bursts.

D. The system becomes unfair by always running the shortest job first.

Solution

1. Step 1: Understand effect of large time quantum

   If the quantum is very large, each process runs almost to completion before switching, similar to First-Come-First-Served scheduling.

2. Step 2: Analyze performance impact

   This causes longer wait times for other processes and reduces the fairness and responsiveness of Round Robin.

3. Final Answer:

   It behaves like First-Come-First-Served, causing longer wait times for some processes. -> Option A

4. Quick Check:

   Large quantum = FCFS behavior, longer waits [OK]

Hint: Large quantum makes Round Robin act like FCFS [OK]

Common Mistakes:

• Thinking large quantum reduces overhead
• Assuming all processes finish faster
• Confusing with shortest job first scheduling