FCFS Scheduling Algorithm in Operating System

• Non-preemptive Scheduling: Once a process starts executing, it will not be interrupted until completion.
• First Come, First Served: The process that arrives first will be executed first, similar to a queue in real life.
• Fairness: FCFS is fair in terms of the order of execution; each process is executed in the order it arrives.
• Burst Time: The total time a process needs to complete its execution. It is a key factor in determining the total time a process will spend in the system.

Comparison with Other Scheduling Algorithms

Let’s compare FCFS with some other popular scheduling algorithms to better understand its limitations and advantages.

1. FCFS vs. Shortest Job First (SJF)

SJF scheduling is another non-preemptive algorithm, but it schedules processes based on their burst time. The process with the shortest burst time is executed first. Compared to FCFS:

• Waiting Time: SJF reduces the waiting time significantly compared to FCFS, especially in cases where short jobs come after long jobs.
• Convoy Effect: SJF minimizes the convoy effect because shorter jobs are given preference.
• Drawback: However, SJF can be hard to implement because the operating system needs to know the burst time of processes in advance, which is not always feasible.

2. FCFS vs. Round Robin (RR)

Round Robin (RR) is a preemptive algorithm that allocates the CPU to each process for a fixed time slice, or quantum. After the time slice is over, the CPU is given to the next process in the ready queue.

• Fairness: Round Robin is more responsive to all processes since it divides the CPU time equally.
• FCFS: In FCFS, processes can suffer from long waiting times if long processes arrive first, whereas RR ensures that each process gets a fair share of CPU time.
• Efficiency: FCFS can be more efficient than RR if there are few processes or if the processes have similar burst times.

3. FCFS vs. Priority Scheduling

Priority Scheduling assigns priority levels to each process. Processes with higher priority are executed first. If two processes have the same priority, FCFS is used to decide the order of execution.

• Customization: Priority Scheduling allows more customization based on process importance, whereas FCFS is simple but lacks flexibility.
• Efficiency: Priority Scheduling can be more efficient in systems where certain processes are critical, but it can suffer from starvation if low-priority processes are always preempted.

Real-World Applications of FCFS Scheduling

FCFS may not always be the most efficient in modern operating systems, but it can still be useful in specific scenarios:

• Batch Processing: In scenarios where jobs are submitted in batches and the order doesn’t matter, FCFS can be effective.
• Non-Interactive Systems: For systems where real-time or interactive performance is not a priority, FCFS can provide a straightforward scheduling method.
• Simple Use Cases: FCFS can be used in simple embedded systems or systems with low process load.

Final Thoughts:

The FCFS Scheduling Algorithm offers a simple and intuitive approach to process management in operating systems. While it guarantees fairness by giving each process a turn based on their arrival time, its limitations – particularly the convoy effect and long waiting times – make it unsuitable for real-time and interactive applications.

Understanding the strengths and weaknesses of FCFS can help developers choose the best scheduling algorithm based on their specific system requirements.