First Come First Served Process Scheduling FCFS in operating systems

First Come First Served Scheduling (FCFS)

Process arrives first always execute first.

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

FCFS is pre-emptive scheduling algorithm
If 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.

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

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;

}