First Come First Served Scheduling


In this topic, you will learn about, First Come First Served (FCFS) Scheduling.

First Come First Served (FCFS) Scheduling: It is the simplest CPU scheduling algorithm with this scheme, the process that requests the CPU first is allocated the CPU first. It implements a FIFO queue. When a process enters the ready queue, it is linked to the tail of the queue. When the CPU is free, it is allocated to the process at the head of the queue. The running process is then removed from the queue.

The FCFS scheduling algorithm performance can be measured by the following examples:

Process         Burst Time
P1                    18
P2                     3
P3                     3

Considering the set of process arrived at time zero. If the processes arrived in order P1, P2, P3 and are served in FCFS order, we get the result shown in the following grand chart.

First Come First Served Scheduling
First Come First Served Scheduling Table

The FCFS scheduling algorithm is non-primitive i.e. Once the CPU is allocated to a process, that process keeps the CPU until it releases the CPU, either by terminating or by requesting input-output.

Note: It would be a disaster to allow one process to keep the CPU for an extended period.

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