FCFS (First Come First Served) in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the basic principle of FCFS scheduling

Which statement best describes how the FCFS (First Come First Served) scheduling algorithm works?

A Processes with the shortest burst time are scheduled first.

B Processes are scheduled in the order they arrive, without preemption.

C Processes are scheduled based on their priority levels.

D Processes are scheduled randomly to ensure fairness.

💡 Hint

Think about the meaning of 'First Come First Served' in everyday life.

FCFS schedules processes in the order they arrive, running each to completion before moving to the next. It does not preempt running processes.

🔍 Analysis

intermediate

Calculating average waiting time in FCFS

Given three processes with burst times 5, 3, and 8 milliseconds arriving in that order, what is the average waiting time using FCFS scheduling?

A 4 milliseconds

B 3 milliseconds

C 6 milliseconds

D 5 milliseconds

💡 Hint

Calculate waiting time for each process and then find the average.

Waiting times: P1=0, P2=5, P3=8. Average = (0+5+8)/3 = 13/3 ≈ 4.33 ms, rounded to 4 ms.

❓ Comparison

advanced

Comparing FCFS with other scheduling algorithms

Which of the following is a major disadvantage of FCFS compared to Shortest Job First (SJF) scheduling?

A FCFS always results in the minimum average waiting time.

B FCFS requires knowledge of process burst times in advance.

C FCFS can cause long waiting times for short processes if a long process arrives first.

D FCFS preempts processes frequently, causing overhead.

💡 Hint

Consider how FCFS handles processes of different lengths arriving in sequence.

FCFS can lead to the 'convoy effect' where short processes wait behind long ones, increasing average waiting time compared to SJF.

❓ Reasoning

advanced

Identifying the impact of process arrival times in FCFS

Consider three processes arriving at times 0, 2, and 4 seconds with burst times 4, 3, and 1 seconds respectively. Using FCFS, what is the waiting time for the third process?

A 3 seconds

B 5 seconds

C 0 seconds

D 4 seconds

💡 Hint

Calculate when the third process starts after the first two finish.

Process 1 runs from 0 to 4, process 2 from 4 to 7, so process 3 starts at 7. It arrived at 4, so waiting time = 7 - 4 = 3 seconds.

📋 Factual

expert

Identifying starvation in FCFS scheduling

Which statement about starvation in FCFS scheduling is true?

A Starvation is common in FCFS because it uses dynamic priorities.

B Starvation occurs frequently in FCFS due to priority inversion.

C Starvation occurs in FCFS when short processes are repeatedly preempted by long ones.

D Starvation cannot occur in FCFS because processes are served in arrival order.

💡 Hint

Think about how FCFS treats all processes equally based on arrival time.

FCFS serves processes strictly in arrival order without preemption or priority, so starvation does not occur.