First Come First Serve CPU Scheduling

First Come First Serve (FCFS) CPU Scheduling is one of the simplest and most straightforward algorithms used in operating systems to determine the execution order of processes. With FCFS, the processes are executed in the order they arrive, like waiting in line at a grocery store. This algorithm is easy to implement and provides a fair distribution of resources, but it can suffer from long waiting times for processes with higher burst times.

FCFS has a long history in the world of CPU scheduling. It was one of the earliest scheduling algorithms to be developed, dating back to the early days of computing. Despite its simplicity, FCFS still finds use in scenarios where fairness and simplicity are more important than performance optimization. However, it is important to note that FCFS is not optimal in terms of minimizing waiting times and response times. In situations where the arrival times and burst times of processes are unpredictable or vary greatly, other algorithms like Round Robin or Shortest Job Next may be more efficient alternatives.

The Basics of First Come First Serve CPU Scheduling

First Come First Serve (FCFS) CPU Scheduling is one of the simplest and most straightforward CPU scheduling algorithms used in operating systems. As the name suggests, this algorithm schedules processes based on the order in which they arrive in the ready queue. The first process that arrives is the first to be executed by the CPU, hence the name "First Come First Serve". FCFS operates on a non-preemptive basis, meaning once a process starts executing, it will continue until it completes or gets blocked. This article will delve into the details of FCFS CPU scheduling, its advantages, limitations, and scenarios where it is best suited.

How FCFS CPU Scheduling Works

FCFS CPU Scheduling works on the principle of a queue data structure. When a process arrives, it is added to the back of the queue. The CPU selects the process at the front of the queue for execution and continues with it until it finishes its execution or gets blocked. Once the process completes, the CPU selects the next process in the queue for execution. This continues until all processes have been executed.

The queue used in FCFS scheduling is known as the ready queue. It contains all the processes waiting for execution. The processes are placed in the queue in the order they arrive, forming a "first in, first out" (FIFO) order. The scheduling policy of FCFS is non-preemptive, which means the executing process is not interrupted until it finishes or gets blocked.

One key point to note about FCFS scheduling is that it is highly dependent on the order of process arrival. If a long process arrives first, it will hold the CPU for an extended period, even if shorter processes arrive later. This can lead to poor efficiency and increased waiting times for subsequent processes.

Advantages of FCFS CPU Scheduling

FCFS CPU Scheduling has several advantages that make it a suitable choice in certain scenarios:

• Simple and easy to implement: FCFS is one of the simplest CPU scheduling algorithms to implement. It is easy to understand and does not require complex computations or data structures.
• Fairness: FCFS provides fairness in scheduling, as it follows a strict "first come, first served" order. Each process gets an equal opportunity to execute.
• No starvation: FCFS guarantees that every process will eventually get CPU time. There is no starvation, as long as processes keep arriving.
• No overhead: FCFS does not involve any context switching or additional overhead associated with preemption. Once a process starts execution, it continues without interruption until completion or blocking.

Limitations of FCFS CPU Scheduling

While FCFS CPU Scheduling has its advantages, it also has some limitations that need to be considered:

• No optimization for process characteristics: FCFS does not take into account any characteristics of the processes, such as their burst time or priority. This can lead to suboptimal scheduling in certain scenarios.
• Long waiting times: If a long process arrives first, shorter processes that arrive later have to wait until the long process completes. This can result in increased waiting times and reduced overall efficiency.
• Lack of interactivity: FCFS scheduling does not prioritize interactive processes that require immediate response. Interactive processes may have to wait until all preceding processes finish their execution.
• No utilization of CPU bursts: FCFS does not consider the length of CPU bursts or the potential for blocking during the execution of a process. It treats all processes equally, regardless of their resource requirements.

Optimizing FCFS CPU Scheduling

While FCFS CPU Scheduling is simple and fair, it may not always be the most optimal choice for all scenarios. However, there are ways to optimize its performance:

Implementing Prioritization

One approach to optimize FCFS is by implementing priority levels for processes. Instead of executing all processes in the order they arrive, the CPU can prioritize processes based on their importance or urgency. This ensures that critical or time-sensitive processes get executed first, even if they arrive later in the queue.

By introducing priorities, the FCFS algorithm can be enhanced to dynamically adjust the order in which processes are executed, taking into account their significance and requirements. This helps in better resource utilization and improved overall system performance.

Implementing prioritization can be done by assigning a priority value to each process and updating the ready queue based on those priorities. When the CPU selects a process for execution, it chooses the one with the highest priority from the available processes.

Combining FCFS with Other Scheduling Algorithms

Another way to optimize FCFS is by combining it with other scheduling algorithms. This hybrid approach can take advantage of the strengths of different algorithms to achieve better results.

For example, one hybrid approach is using a mix of FCFS and Round Robin (RR) scheduling. In this approach, short duration processes are scheduled using the RR algorithm to ensure fairness and quick response times. Longer duration processes are handled using the FCFS algorithm to prevent excessive context switching.

By combining different scheduling algorithms, it is possible to strike a balance between fairness, efficiency, and response times, depending on the specific requirements of the system.

Conclusion

First Come First Serve (FCFS) CPU Scheduling is a simple and straightforward algorithm that operates on a non-preemptive basis. While it provides fairness and eliminates starvation, it can result in longer waiting times and may not optimize resource utilization. However, by implementing prioritization or combining it with other scheduling algorithms, the performance of FCFS can be optimized to better suit specific requirements. Understanding the strengths and limitations of FCFS CPU Scheduling allows for informed decision-making in choosing the appropriate scheduling algorithm for a system's particular needs.

Overview of First Come First Serve CPU Scheduling

First Come First Serve (FCFS) is a non-preemptive CPU scheduling algorithm used in operating systems. It is a simple and intuitive algorithm that schedules processes based on their arrival time. The process that arrives first is executed first, hence the name "First Come First Serve".

How FCFS Scheduling Works

In FCFS scheduling, the ready queue acts as a simple queue data structure. When a process arrives, it is added to the end of the queue. The CPU selects the process at the front of the queue and executes it until completion. Once the process finishes, the CPU moves on to the next process in the queue. FCFS has the benefit of simplicity and fairness, as it ensures that every process gets its turn in the order it arrived. However, it suffers from a major drawback known as the "convoy effect". If a long process arrives first, all subsequent shorter processes have to wait, leading to potential delays and inefficiency.

Pros and Cons of FCFS Scheduling

Pros	Cons
Simple to implement	Can lead to longer waiting times for shorter processes
Fairness in execution	The convoy effect can cause inefficiency
Best suited for batch processing systems	Lacks flexibility for real-time systems

Conclusion

First Come First Serve CPU Scheduling is a simple and fair algorithm that executes processes based on their arrival time. While it is easy to implement and ensures fairness, it has limitations such as longer waiting times

Frequently Asked Questions

In this section, we have answered some frequently asked questions about First Come First Serve CPU Scheduling.

1. How does First Come First Serve (FCFS) CPU Scheduling work?

FCFS CPU Scheduling is a non-preemptive scheduling algorithm where processes are executed in the order they arrive. The process that arrives first gets executed first. Once a process starts its execution, it keeps running until it finishes or it is interrupted by an event or another process.

When a process completes its execution, the next process in the queue is chosen for execution. This continues until all the processes are completed. The waiting time for each process is determined by the sum of the burst times of all preceding processes.

2. What are the advantages of First Come First Serve CPU Scheduling?

One of the advantages of FCFS CPU Scheduling is its simplicity. The algorithm is easy to understand and implement, making it a good choice for simpler systems.

Another advantage is that FCFS ensures fairness, as the processes are executed in the order they arrive. This can be beneficial in scenarios where all processes have similar priorities, and it is fair to execute them based on their arrival time.

3. What are the limitations of First Come First Serve CPU Scheduling?

One major limitation of FCFS CPU Scheduling is that it can lead to poor performance in terms of waiting time. If a long process arrives first, all the subsequent processes have to wait for a significant amount of time, resulting in high waiting times.

Additionally, FCFS is not suitable for scenarios where shorter processes arrive after longer ones. This can lead to a phenomenon known as "convoy effect," where shorter processes get stuck behind longer processes, causing longer waiting times.

4. Can FCFS CPU Scheduling cause starvation?

No, FCFS CPU Scheduling does not cause starvation. Since processes are executed in the order they arrive, all processes get a fair chance to execute. However, it is important to note that FCFS can lead to high waiting times for some processes, which may give the impression of starvation.

Starvation occurs when a process keeps waiting indefinitely to get CPU time, while other processes are executing. This is not the case with FCFS as each process eventually gets CPU time, although some may have to wait for longer periods.

5. When is First Come First Serve CPU Scheduling not suitable?

FCFS CPU Scheduling is not suitable for scenarios where the arrival times of processes are unpredictable. If processes with shorter execution times arrive after processes with longer execution times, it can result in longer waiting times and decreased overall system performance. In such cases, other scheduling algorithms like Shortest Job First (SJF) or Priority Scheduling might be more appropriate.

Additionally, FCFS may not be suitable for real-time systems or systems with strict response time requirements, as it does not prioritize processes based on their urgency or importance.

In conclusion, First Come First Serve (FCFS) CPU scheduling is a simple and fair method of allocating CPU time to different processes. It follows a straightforward approach of serving the processes in the order they arrive. This scheduling algorithm is beneficial in scenarios where there are no defined priorities or time requirements for the processes.

The FCFS algorithm ensures that each process gets its fair share of CPU time without any bias or preference. However, it can lead to long waiting times for processes that arrive later, causing potential delays and decreased overall system performance. Despite its limitations, FCFS remains a popular choice due to its simplicity and transparency in resource allocation.