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First Come First Serve
- 1. Welcome to the Presentation of Presented by: Edwin Makeu Presented to: Mrs Rupali & BCA 2 DT 01st Feb 2017 First Come First Serve Scheduling Algorithm
- 2. Content •What is First Come First Serve Scheduling Algorithm •Basic Concepts of FCFS •Example •Advantages •Disadvantages
- 4. Basic Concepts •Jobs are executed on first come, first serve basis. •It is a non-preemptive scheduling algorithm. •Its implementation is based on FIFO queue.
- 5. Example process Time for which cpu is required CPU burst time P1 10 p2 5 p3 5 P1 P2 P3 0 10 15 20 Waiting Time for P1 = 0 Millisecond Waiting Time for P2 = 10 Millisecond Waiting Time for P2 = 15 Millisecond Average Waiting Time = (0+10+15)/3 = 8.33 Millisecond Gantt chart
- 6. Advantages •Simple •Suitable for batch system. •It is simple to understand and code. •Easy to understand and implement.
- 7. Disadvantage •This scheduling method is non-preemptive •Waiting time can be large if short request wait behind the long process. •It is not suitable for time sharing system. •Poor in performance as average wait time is high
Editor's Notes
- Scheduling algorithm is the algorithm which indicates how much time cpu is allocated to a processes The goal of any SA is to fulfil the number of criteria on how a cpu is to
- FCFS also termed as First-In-First-Out i.e. allocate the CPU in order in which the process arrive. When the CPU is free, it is allowed to process, which is occupying the front of the queue. Once this process goes into running state, its PCB is removed from the queue. This algorithm is non-preemptive. Analogy[edit] A FCFS acts like any normal queue whether, it is a line in a cinema, a checkout line in a store, or a queue for a ticket booth. The first person or process to arrive (First In) is the first one to be dealt with (First Out). If one person goes through the line and then decides they forgot something then they have to go back through. This is exactly how OS's with this design let programs conduct their business. One person (aka: process) at a time. Implementation[edit] To implement this, you can create a queue, an abstract data type (ADT) that can be constructed from a linked list data structure. The system can dequeue the next process from the front of the queue, run the process until completion (or enqueue the process at the end of the line in more complex schemes), then enqueue the process at the end of the line, allowing the next process to use the CPU.
- Examples Consider the following set of processes having their CPU-burst time. CPU burst time indicates that for how much time, the process needs the CPU. If the processes have arrived in order P1, P2, P3 then the average waiting time for process will be obtained from Gantt chart.
- This scheduling method is nonpreemptive, that is, the process will run until it finishes. Because of this nonpreemptive scheduling, short processes which are at the back of the queue have to wait for the long process at the front to finish It is not suitable for time sharing system where it is important that each user should get the CPU for equal amount of time interval.