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First come, first served (FCFS) is an operating system process scheduling algorithm and a network routing management mechanism that automatically executes queued requests and processes by the order of their arrival. With first come, first served, what comes first is handled first; the next request in line will be executed once the one before it is complete.
FCFS is also known as first-in, first-out (FIFO) and first come, first choice (FCFC)
FCFS provides an efficient, simple and error-free process scheduling algorithm that saves valuable CPU resources. It uses nonpreemptive scheduling in which a process is automatically queued and processing occurs according to an incoming request or process order. FCFS derives its concept from real-life customer service.
Let's take a look at how FCFS process scheduling works. Suppose there are three processes in a queue: P1, P2 and P3. P1 is placed in the processing register with a waiting time of zero seconds and 10 seconds for complete processing. The next process, P2, must wait 10 seconds and is placed in the processing cycle until P1 is processed. Assuming that P2 will take 15 seconds to complete, the final process, P3, must wait 25 seconds to be processed. FCFS may not be the fastest process scheduling algorithm, as it does not check for priorities associated with processes. These priorities may depend on the processes' individual execution times.