FCFS (First Come First Served) in Operating Systems - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does FCFS stand for in operating systems?

FCFS stands for First Come First Served. It is a simple scheduling algorithm where the process that arrives first gets executed first.

beginner

How does the FCFS scheduling algorithm decide which process to run next?

FCFS runs processes in the order they arrive. The process that comes first is served first, without preemption.

intermediate

What is a major drawback of the FCFS scheduling algorithm?

A major drawback is the "convoy effect," where short processes wait a long time if a long process is running first, causing poor average waiting time.

beginner

In FCFS, if Process A arrives at time 0 and needs 5 units of CPU, and Process B arrives at time 1 needing 2 units, which process finishes first?

Process B finishes first because Process A starts at time 0 and runs for 5 units, finishing at time 5. Process B starts at time 5 and runs for 2 units, finishing at time 7. So Process A finishes first.

beginner

Is FCFS a preemptive or non-preemptive scheduling algorithm?

FCFS is a non-preemptive scheduling algorithm. Once a process starts running, it runs until it finishes without interruption.

What is the main principle of FCFS scheduling?

A Serve processes randomly

B Serve processes in the order they arrive

C Serve the process with highest priority first

D Serve the shortest process first

FCFS schedules processes based on their arrival time, serving the earliest arriving process first.

Which problem is commonly associated with FCFS scheduling?

A Convoy effect

B Starvation

C Deadlock

D Priority inversion

The convoy effect happens in FCFS when short processes wait behind long ones, causing delays.

Is FCFS scheduling preemptive or non-preemptive?

A Preemptive

B Both

C Non-preemptive

D Depends on the process

FCFS is non-preemptive; once a process starts, it runs until completion.

If Process X arrives before Process Y, which process will FCFS run first?

A Randomly chosen

B Process Y

C The one with shorter burst time

D Process X

FCFS runs the process that arrives first, so Process X runs before Process Y.

Which of these is NOT a characteristic of FCFS?

A Processes can be interrupted

B Can cause long waiting times

C Simple to implement

D Non-preemptive scheduling

FCFS does not interrupt processes once they start; it is non-preemptive.

Explain how the FCFS scheduling algorithm works and mention one advantage and one disadvantage.

Think about the order processes arrive and how that affects waiting times.

Describe a real-life situation that is similar to FCFS scheduling.

Imagine a queue where everyone waits their turn.