Scheduling Algorithms

Notice that the long process P₁ will prevent the rest of the processes from running on the CPU for 24 milliseconds. Specifically, the average waiting time in this schedule is (0 + 24 + 27) / 3 = 17 milliseconds. The average response time in this case is the same as the average waiting time, which is (0 + 24 + 27) / 3 = 17 ms.

If processes P₂ and P₃ would arrive just before P₁, the schedule would be much different:

Above, since the smaller processes get to complete the first, the average waiting time drops to (0 + 3 + 6)/3 = 3 milliseconds. In other words, the average waiting time highly depends on when each process arrives.