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.
| 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
| 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++
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#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; } |