First-Come First-Serve Scheduling, FCFS

First-come, first-served (FCFS): – sometimes first-in, first-served and first-come, first choice – is a service policy whereby the requests of customers or clients are attended to in the order that they arrived, without other biases or preferences. The policy can be employed when processing sales orders, in determining restaurant seating, on a taxi stand, etc. In Western society, it is the standard policy for the processing of most queues in which people wait for a service that was not prearranged or pre-planned.

Example:
















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

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