FCFS (First Come First Served)

Last updated on Apr 5, 2023

FCFS, or First Come First Served, is a scheduling algorithm that is used in various fields such as computer science, operations research, and management. The basic idea behind FCFS is that the tasks or jobs that arrive first are served or processed first, without any prioritization based on their size, importance, or duration. In this way, the FCFS algorithm is often described as non-preemptive because once a task is started, it continues until it is completed.

The FCFS algorithm is used in many different contexts, ranging from CPU scheduling in operating systems to queue management in customer service. In this article, we will explore the FCFS algorithm in more detail, examining its advantages, disadvantages, and real-world applications.

How does FCFS work?

The FCFS algorithm is based on the simple idea of serving tasks in the order that they arrive. In a computer system, this means that the CPU serves each task in the order that they are submitted to the system, without any attempt to prioritize them based on their characteristics. For example, a small task that takes only a few seconds to complete will be served after a long-running task that takes several minutes to complete, as long as the long-running task was submitted to the system first.

The FCFS algorithm can be illustrated using a simple example. Suppose that we have a CPU that can only process one task at a time, and three tasks are submitted to the system in the following order:

Task A: Takes 5 seconds to complete Task B: Takes 2 seconds to complete Task C: Takes 3 seconds to complete

Using the FCFS algorithm, the tasks would be served in the following order:

Task A: Begins processing immediately and takes 5 seconds to complete
Task B: Begins processing once Task A is complete and takes 2 seconds to complete
Task C: Begins processing once Task B is complete and takes 3 seconds to complete

As you can see, the FCFS algorithm processes the tasks in the order that they were submitted to the system, without any attempt to prioritize them based on their size or duration.

Advantages of FCFS

One of the primary advantages of the FCFS algorithm is its simplicity. Because the algorithm is based on a straightforward concept of serving tasks in the order that they arrive, it is easy to implement and does not require complex logic or algorithms. This simplicity makes the FCFS algorithm an attractive option for many applications, especially in situations where the complexity of other algorithms may not be necessary.

Another advantage of the FCFS algorithm is that it is fair. Because tasks are served in the order that they arrive, there is no bias towards any particular task or user. This fairness can be especially important in situations where multiple users or processes are competing for resources, such as in a multi-user operating system or a shared network.

Disadvantages of FCFS

While the FCFS algorithm has some advantages, it also has several disadvantages that can limit its usefulness in certain situations. One of the primary disadvantages of the FCFS algorithm is that it does not take into account the size or duration of tasks. This means that long-running tasks can cause other tasks to wait for extended periods, even if they are small and could be completed quickly.

Another disadvantage of the FCFS algorithm is that it can lead to high average waiting times. This is because long-running tasks can cause a backlog of other tasks to build up, leading to longer wait times for all tasks. In situations where fast response times are critical, such as in real-time systems or high-performance computing, the FCFS algorithm may not be the best choice.

Real-world applications of FCFS

The FCFS algorithm is used in many real-world applications, ranging from CPU scheduling in operating systems to queue management in customer service. In this section, we will explore some of the common applications of the FCFS algorithm in more detail.

CPU scheduling

One of the primary applications of the FCFS algorithm is in CPU scheduling in operating systems. In this context, the FCFS algorithm is used to determine the order in which processes are executed by the CPU. When a process is submitted to the system, it is added to the end of the queue and is processed in the order that it was received. Once a process starts executing, it continues until it is complete, unless it is preempted by a higher-priority process.

While the FCFS algorithm is simple and fair, it can lead to long average waiting times and poor performance in some situations. For example, if a long-running process is submitted to the system, it can cause other processes to wait for extended periods, leading to longer average waiting times and poorer performance overall. To address these issues, many modern operating systems use more sophisticated scheduling algorithms that take into account factors such as process priority, execution time, and I/O requirements.

Queue management

The FCFS algorithm is also commonly used in queue management systems, such as those used in customer service or retail environments. In this context, the FCFS algorithm is used to determine the order in which customers are served or processed by the system. When a customer arrives, they are added to the end of the queue and are served in the order that they arrived. Once a customer is served, they are removed from the queue and the next customer in line is served.

While the FCFS algorithm is simple and fair, it can lead to long waiting times for customers, especially in situations where there are long lines or a large number of customers. To address these issues, many modern queue management systems use more sophisticated algorithms that take into account factors such as customer priority, service time, and queue length.

Batch processing

The FCFS algorithm is also commonly used in batch processing systems, such as those used in manufacturing or logistics. In this context, the FCFS algorithm is used to determine the order in which tasks or jobs are processed by the system. When a job is submitted to the system, it is added to the end of the queue and is processed in the order that it was received. Once a job is complete, the next job in line is processed.

While the FCFS algorithm is simple and fair, it can lead to long processing times for large or complex jobs, which can cause delays for subsequent jobs. To address these issues, many modern batch processing systems use more sophisticated scheduling algorithms that take into account factors such as job priority, processing time, and resource availability.

Conclusion

In conclusion, the FCFS algorithm is a simple and fair scheduling algorithm that is widely used in many different contexts, ranging from CPU scheduling in operating systems to queue management in customer service. While the FCFS algorithm has some advantages, such as its simplicity and fairness, it also has several disadvantages that can limit its usefulness in certain situations, such as its inability to prioritize tasks based on their size or duration. To address these issues, many modern scheduling algorithms use more sophisticated algorithms that take into account a wider range of factors, such as process priority, execution time, and resource availability.