What is SJF scheduling example?

Shortest Job First (SJF) Scheduling However, SJF scheduling algorithm, schedules the processes according to their burst time. In SJF scheduling, the process with the lowest burst time, among the list of available processes in the ready queue, is going to be scheduled next.

What is SJF scheduling algorithm in OS?

Shortest Job First (SJF) is an algorithm in which the process having the smallest execution time is chosen for the next execution. This scheduling method can be preemptive or non-preemptive. It significantly reduces the average waiting time for other processes awaiting execution.

What is SJF in CPU scheduling?

The shortest job first (SJF) or shortest job next, is a scheduling policy that selects the waiting process with the smallest execution time to execute next. SJN, also known as Shortest Job Next (SJN), can be preemptive or non-preemptive.

How does SJF calculate finish time?

Turnaround Time = Total Turnaround Time- Arrival Time P1 = 28 – 0 =28 ms, P2 = 5 – 1 = 4, P3 = 13 – 2 = 11, P4 = 20 – 3 = 17, P5 = 8 – 4 = 4 Total Turnaround Time= 64 mills.

How is SJF algorithm implemented?

Algorithm of SJF Select the process with minimum arrival time as well as minimum burst time. After completion of the process, select from the ready queue the process which has the minimum burst time. Repeat above processes untill all processes have finished their execution.

What are the advantages and disadvantages of SJF scheduling?

Shortest Job First (SJF) [Preemptive and Non- Preemptive]:

  • Advantages – Shortest jobs are favored. It is provably optimal, in that it gives the minimum average waiting time for a given set of processes.
  • Disadvantages – SJF may cause starvation, if shorter processes keep coming. This problem is solved by aging.

Why is SJF optimal?

SJF is provably optimal, in that for a given set of processes and their CPU bursts/execution times it gives the least average waiting time for each process.

What is preemptive and non-preemptive scheduling?

In preemptive scheduling, the CPU is allocated to the processes for a limited time whereas, in Non-preemptive scheduling, the CPU is allocated to the process till it terminates or switches to the waiting state.

What is non-preemptive scheduling?

Non-preemptive Scheduling is a CPU scheduling technique the process takes the resource (CPU time) and holds it till the process gets terminated or is pushed to the waiting state. No process is interrupted until it is completed, and after that processor switches to another process.

What is the advantage of SJF?

Advantages of SJF Reduces average waiting time. Helpful for batch-type processing where runtimes are known in advance. For long-term scheduling, we can obtain a burst time estimate from the job description. It is necessary to predict the value of the next burst time for Short-Term Scheduling.

What is the drawback of SJF scheduling?

SJF may cause starvation, if shorter processes keep coming. This problem is solved by aging. It cannot be implemented at the level of short term CPU scheduling.

How is SJF scheduling calculated?

Waiting Time =Total waiting Time – No. of Milisec. Process executed – Arrival Time P1 = 20 – 1 – 0 = 19 ms, P2 = 4 – 3 – 1 = 0 ms, P3 = 8 – 0 – 2 = 6ms P4 = 13 – 0 – 3 = 10 ms, P5 = 5 – 0 – 4 = 1 ms. Total Waiting Time = 36 mills.

What is burst time in OS?

Burst Time refers to the time required in milli seconds by a process for its execution. The Burst Time takes into consideration the CPU time of a process. The I/O time is not taken into consideration. It is called as the execution time or running time of the process.

Which scheduling is best in OS?

The FCFS is better for a small burst time. The SJF is better if the process comes to processor simultaneously. The last algorithm, Round Robin, is better to adjust the average waiting time desired.

What is FIFO algorithm in OS?

First In First Out (FIFO) – This is the simplest page replacement algorithm. In this algorithm, the operating system keeps track of all pages in the memory in a queue, the oldest page is in the front of the queue. When a page needs to be replaced page in the front of the queue is selected for removal.