Interview Prepoperating-systemseasyAmazonWiproTCS

FCFS Scheduling - Convoy Effect & Waiting Time

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Solution Trace

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Steps

setup

Initialize Processes and Ready Queue

All processes are created with their arrival and burst times. The ready queue is empty initially because only P1 has arrived at time 0.

💡 Initialization sets the stage for scheduling by defining process attributes and starting conditions.

Line:

processes = [P1, P2, P3, P4]
current_time = 0
ready_queue = []

💡 Processes have arrival times and burst times; scheduling starts at time 0 with processes that have arrived.

class Process:
    def __init__(self, pid, arrival, burst):
        self.pid = pid
        self.arrival = arrival
        self.burst = burst
        self.remaining = burst
        self.state = 'new'

processes = [Process('P1',0,5), Process('P2',1,3), Process('P3',2,8), Process('P4',3,6)]
current_time = 0
ready_queue = []
completed = []

# STEP 1: Initialize ready queue with processes arrived at time 0
for p in processes:
    if p.arrival <= current_time:
        p.state = 'ready'
        ready_queue.append(p)

while ready_queue:
    # STEP 2: Pick first process in ready queue
    current = ready_queue.pop(0)
    current.state = 'running'
    # STEP 3: Run process to completion
    current_time = max(current_time, current.arrival) + current.burst
    current.remaining = 0
    current.state = 'terminated'
    completed.append(current)
    # STEP 4: Add newly arrived processes to ready queue
    for p in processes:
        if p.state == 'new' and p.arrival <= current_time:
            p.state = 'ready'
            ready_queue.append(p)

# STEP 5: Calculate waiting and turnaround times
waiting_times = []
turnaround_times = []
start_time = 0
for p in completed:
    wait = start_time - p.arrival
    if wait < 0:
        wait = 0
    turnaround = wait + p.burst
    waiting_times.append(wait)
    turnaround_times.append(turnaround)
    start_time += p.burst

avg_waiting_time = sum(waiting_times) / len(waiting_times)
avg_turnaround_time = sum(turnaround_times) / len(turnaround_times)

# STEP 6: Output results
print(f"Average Waiting Time = {avg_waiting_time}")
print(f"Average Turnaround Time = {avg_turnaround_time}")

📊

FCFS Scheduling - Convoy Effect & Waiting Time - Watch the Algorithm Execute, Step by Step

Watching the algorithm step-by-step reveals how process order and burst times affect waiting times, which is hard to grasp from code alone.

Step 1/11

·Active fill★Answer cell

Transition new → ready pid:P1 - arrival at time 0

ready

burst: 5

new

burst: 3

new

burst: 8

new

burst: 6

Ready Queue

Waiting Queue

P2 (arrival_time)P3 (arrival_time)P4 (arrival_time)

🖥CPUidlet=0

Practice

(1/5)

1. Which of the following is a major trade-off when using indexed file allocation compared to contiguous allocation?

medium

A. Indexed allocation requires additional disk space for index blocks, increasing overhead

B. Indexed allocation causes more external fragmentation than contiguous allocation

C. Indexed allocation cannot support direct access to file blocks

D. Indexed allocation always results in slower sequential access than linked allocation

Start learning this pattern below

Initialize Processes and Ready Queue

Start Running P1

Advance Time to 5, P1 Completes

Start Running P2

Advance Time to 8, P2 Completes

Start Running P3

Advance Time to 16, P3 Completes

Start Running P4

Advance Time to 22, P4 Completes

Calculate Waiting and Turnaround Times

Display Final Average Waiting and Turnaround Times

Key Takeaways

Practice

Solution

Step 1: Understand indexed allocation overhead

Step 2: Analyze indexed allocation requires additional disk space for index blocks, increasing overhead

Step 3: Analyze indexed allocation causes more external fragmentation than contiguous allocation

Step 4: Analyze indexed allocation cannot support direct access to file blocks

Step 5: Analyze indexed allocation always results in slower sequential access than linked allocation

Final Answer:

Quick Check:

Solution

Step 1: Understand Ready state resource usage

Step 2: Analyze each option

Final Answer:

Quick Check:

Solution

Step 1: Understand starvation in non-preemptive SJF

Step 2: Analyze other options

Final Answer:

Quick Check:

Solution

Step 1: Recall Banker's Algorithm assumptions

Step 2: Analyze the scenario

Step 3: Evaluate options

Final Answer:

Quick Check:

Solution

Step 1: Identify internal fragmentation cause

Step 2: Evaluate strategies

Step 3: Analyze other options

Final Answer:

Quick Check: