FCFS CPU Scheduling in OS

When it comes to scheduling, FCFS is the most basic and simplest algorithm. It is, however, not very good for time sharing systems because it does not prioritize tasks and has high waiting times. If you are using this algorithm, you will want to follow the steps below:

FCFS is the easiest and simplest scheduling algorithm

The FCFS scheduling algorithm is the simplest of CPU scheduling algorithms. It uses a black box to represent the idle time of the CPU. The process that has the lowest arrival time goes first in the ready queue, and the CPU then schedules it first. The FCFS algorithm also calculates the average turn around time and waiting time for the CPU. This allows the OS to determine the efficiency of its scheduling algorithm.

The Shortest Job First (SJF) scheduling algorithm is the most commonly used non-preemptive schedule. It prioritizes processes based on their shortest burst and completion times. It can reduce the average wait time for other processes while increasing the overall throughput. FCFS has some disadvantages compared to SJF, however. In addition to requiring the CPU to learn about its arrival and exit times, FCFS causes more context switching.

FCFS is an OS-based scheduling algorithm that prioritizes processes according to their arrival time. It utilizes a FIFO queue to manage requests. When a process arrives in the queue, it links its PCB with the tail of the queue. When a CPU becomes available, it assigns it to the first process in the queue. As a result, the CPU will be allocated to the process with the shortest arrival time.

FCFS has a few disadvantages. It’s non-preemptive, which means that it will never release the CPU until it finishes processing the previous order. FCFS can handle three requests at once: P1 has a very complex process, P2 is simpler, and P3 is moderately simple. The algorithm is more efficient, but it also requires a higher average wait time.

It does not prioritize tasks

The main reason why FCFS CPU Scheduling in OS doesn’t prioritize tasks is that it breaks ties between processes. In preemptive mode, the waiting time of the highest priority process is zero. However, this is not true for non-preemptive mode. Another major problem with FCFS is that it causes indefinite blocking and starvation. This means that the CPU is likely to be consumed by multiple processes that are not of the same priority.

The two main methods for CPU scheduling are SJF and FCFS. SJF prioritizes processes based on their elapsed time and FCFS is better for shorter durations. Both are based on priority. SJF can lead to starvation since small jobs take priority over large jobs. Furthermore, new small jobs can arrive before the previous ones are finished. FCFS also prevents the occurrence of preemption, which is the process of checking if a scheduled process is still running and has any changes.

FCFS is a common algorithm used in OSs. It uses the First Come, First Served (FCFS) algorithm to schedule tasks. Using FCFS, it will prioritize tasks based on estimated time, rather than on priority or complexity. FCFS is efficient in systems where tasks are similar, but in more complex systems, it might get stuck behind a complex task. This can lead to unpredictable, high-volume performance.

FCFS CPU Scheduling in OS does work by assigning CPUs to processes that request them. It is also managed by a FIFO queue. In FCFS, the CPU is allocated to the process whose queue has the lowest starting time. It offers both a preemptive and non-preemptive algorithm. FCFS is an easy algorithm to implement, but it suffers from high wait time and performance.

It has high waiting times

A common issue facing operating systems is that it has high waiting times for FCFS CPU scheduling. This is because the operating system uses the First Come First Serve (FCFS) scheduling algorithm. This algorithm assigns CPU time to processes starting at 0th second. The average waiting time for three processes is 5.0 milliseconds. The waiting time increases when more than one process is running at a time.

The CPU scheduling algorithm that FCFS uses sorts processes in an order of decreasing arrival time. The process with the shortest arrival time comes first in the ready queue. It gets scheduled first by the CPU. Its average waiting time is a measure of the scheduling algorithm’s effectiveness. This example shows how FCFS performs in a queue. The first process in the queue, P4, will be served before the second one.

This method is easy to implement but has a high waiting time. For example, if three processes arrive simultaneously at a movie theater, the person who arrives first will get the ticket first. Then, the next person will come, and so on. The process will proceed in a similar manner. Those who arrive first will be given priority. Those who arrive second will be assigned CPU resources.

The Shortest Job First algorithm is also used for CPU scheduling. This algorithm assigns CPU time to the waiting process with the lowest execution time. This algorithm is preemptive and may reduce the average waiting time for other processes. If many smaller processes are being added to the queue, it may cause starvation of longer processes. Instead, it may solve the problem by using the concept of ageing. There are many benefits and drawbacks to LJF.

It is not ideal for time-sharing systems

As the name suggests, FCFS is a non-preemptive CPU scheduling algorithm. It will never release a CPU until a process at the front of the queue completes. The problem with FCFS is its high Average Waiting Time, which means that short processes in the back of the queue have to wait for long processes at the front. It is not a good scheduling algorithm for time-sharing systems, as it results in a convoy effect.

Although FCFS is easy to implement, this method has many shortcomings. The biggest is the long wait time. This is analogous to buying a movie ticket at a counter. First person in line buys the ticket. Second person, third person, and fourth person will then buy the ticket. The CPU process works in a similar way. In the event that an algorithm is not correct, a lower priority thread is run.

FCFS and LJF are both CPU scheduling algorithms. While FCFS is the most commonly used, it is not ideal for time-sharing systems. LJF CPU scheduling assigns the CPU to the process with the longest burst time, which is typically the longest. In other words, each process must wait for the entire time before the other processes are given the CPU. Therefore, this algorithm results in long waiting times and a convoy effect.

When determining the CPU scheduler, the system must consider different terms. A minimum turnaround time refers to the amount of time it takes for a process to finish executing. If three processes each take 10 ms, the average turnaround time is 29 ms. Too large a turnaround time degenerates to FCFS. To avoid this, 80% of CPU bursts should be smaller than the time quantum. If this is not possible, multiple queues can be established, and different scheduling algorithms can be used to assign tasks.

It is not as efficient as SJF

Both methods of CPU scheduling work by dividing the total workload into small parts. Each part of the workload is scheduled for execution, and each process is given a set amount of time. The process that takes the least time gets executed first, and the rest follow. This way, the CPU can avoid over-allocating resources by preventing short processes from consuming too much time. However, these two methods have a few drawbacks. FCFS is less efficient, and SJF is more efficient.

A multilevel queue ensures that no single process is left in a waiting state. The CPU is allocated to multiple processes, with each process having a time-slice of X hours. This method prevents starvation, as each process has an equal priority. It is also very useful in situations where multiple processes have different response times. This method can also address the problem of shared memory.

In the OS, CPU scheduling can involve many threads. First-come-first-serve (FIFO) scheduling allocates CPU to the first process on a queue. Because of this, a single process can monopolize the CPU, and run for the maximum amount of time without context switching. SJF is more efficient and is therefore recommended for many users. Further, this method is not as user-friendly.

FCFS is known for its long waiting times. As it is a non-preemptive CPU scheduling algorithm, it processes orders in order of arrival. Therefore, subsequent orders cannot begin processing until the previous one has completed. In addition, the process will never release the CPU until it has completed its execution. The first order may have a large burst time, and subsequent orders must wait for it to finish.