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First-come, First-served Scheduling-computer world

 First-come, First-served Scheduling

In this scheduling algorithm simply the jobs according to their arrival time which job come first in the queue will get the CPU first. It means the process(job) that requests the CPU first is allocate the CPU first. The FCFS policy is simply and easily managed with a FIFO(First in First out) queue. When a process enter in the ready, its PCB is linked onto the tail of the queue. When the CPU is free, it allocated to the process at the head if the queue. The code for FCFS scheduling is very simple to understand. On the negative side, the average waiting time under the FCFS policy is long. The CPU has been allocated to a process, that process keeps CPU its processing is not complete. So the CPU in this scheme is scheduled to the process in the order of arrival at the ready queue it is the simplest CPU scheduling algorithm. 

1. Turn around time :

Turn around time is the time taken by a process between ready queue and finishing execution.

2. Wait time : 

Wait time is the time when a process wait before it's start execution.

3. Burst time: 

Burst time is that time which is taken by a process for its execution on the CPU.

Process P1, P2, P3 it's burst time is in the order 24, 3, 3

If the processes arrive in the order P1, P2, P3 and served in FCFS order. The waiting time for P1 is 0 millisecond, 24 millisecond for process P2, 27 millisecond for process P3. Thus the average waiting time is (0+24+27)/3=17 milliseconds.


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