First Come First Served Process Scheduling FCFS in operating systems

Last modified on February 13th, 2019 at 5:42 pm

First Come First Served Scheduling (FCFS)

In this tutorial, we will try to learn the followings;

What is First Come First Served Scheduling?
Gantt Chart for FCFS
How to calculate turn around time?
FCFS Program in C++
Watch Video Lecture

Process arrives first always execute first.

FCFS is non-preemptive scheduling algorithm so processes priority does not matter.

If the process first arrived is a big process with a high burst time, then other processes with less burst time need to wait.
Average wait time is high.
Easy to implement.
Easy to understand.

Process	Burst Time	Arrival
P1	4	2nd
P2	2	3rd
P3	8	1st
P4	3	4th

Gantt Chart of First Come, First Served (FCFS) Scheduling

Figure: FCFS.

Process	Waiting Time
P1	8
P2	12
P3	0
P4	14

Average Wait Time: (0+8+12+14) / 4 = 8.5

How to calculate turn around time?

TurnAroundTime=BurstTime+WaitingTime.

First Come First Served (FCFS) Program in C++

#include<iostream>

using namespace std;

int main()

{

int n,BurstTime[50],WaitingTime[50],TurnAroundTime[50],AverageWaitingTime=0,AverageTurnAroundTime=0,i,j;

cout<<"Enter total number of processes to demonstrate, Total processes can be from 0 to 50"<<endl;

cin>>n;

cout<<"\nEnter Burst Time for the process: \n";

for(i=0;i<n;i++)

{

cout<<"Process["<<i+1<<"]:";

cin>>BurstTime[i];

}

WaitingTime[0]=0;

//waiting time of first process is initiliazed with 0

// waiting time for each process

for(i=1;i<n;i++)

{

WaitingTime[i]=0;

for(j=0;j<i;j++)

WaitingTime[i]+=BurstTime[j];

}

cout<<"\nProcess\t\tBurst Time\tWaiting Time\tTurnaround Time";

//turnaround time calculation for each process

for(i=0;i<n;i++)

{

TurnAroundTime[i]=BurstTime[i]+WaitingTime[i];

AverageWaitingTime+=WaitingTime[i];

AverageTurnAroundTime+=TurnAroundTime[i];

cout<<"\nProcess["<<i+1<<"]"<<"\t\t"<<BurstTime[i]<<"\t\t"<<WaitingTime[i]<<"\t\t"<<TurnAroundTime[i];

}

AverageWaitingTime/=i;

AverageTurnAroundTime/=i;

cout<<"\n\nAverageerage Waiting Time:"<<AverageWaitingTime;

cout<<"\nAverageerage Turnaround Time:"<<AverageTurnAroundTime;

return 0;

}

First Come First Served Scheduling (FCFS)

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