First-come,First-Served (FCFS) Scheduling

             Process  Burst Time 

                 P1                24

                P2                  3

               P3                  3

• Suppose that the processes arrive in the order: P1 , P2 , P3  
• The Gantt Chart for the schedule is:

• Waiting time for P1  = 0; P2  = 24; P3 = 27
• Average waiting time:  (0 + 24 + 27)/3 = 17
• Suppose that the processes arrive in the order
•    P2 , P3 , P1 .
• 
  
• The Gantt chart for the schedule is:

• Waiting time for P1 = 6; P2 = 0; P3 = 3
• Average waiting time:   (6 + 0 + 3)/3 = 3
• Much better than previous case.
• Convoy effect short process behind long process