FCFS Scheduling

Duration: 10 min

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AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

The video presents a comprehensive educational session on the First Come First Serve (FCFS) CPU scheduling algorithm, a fundamental topic in operating systems. The instructor begins by defining FCFS as the simplest scheduling algorithm, emphasizing that the process requesting the CPU first is allocated the CPU first. Key characteristics are highlighted on the slide: implementation is managed by a FIFO (First In First Out) queue, and the algorithm is always non-preemptive in nature. The instructor uses a visual analogy of a queue at a ticket counter to reinforce the concept. Following the theoretical introduction, the lecture transitions into a practical numerical problem. A table is displayed listing five processes (P0, P1, P2, P3, P4) with their respective Arrival Times (AT) and Burst Times (BT). The instructor systematically solves the problem by first identifying the process with the earliest arrival time (P2 at time 0) to start the execution. He then constructs a Gantt chart at the bottom of the screen to visualize the sequence of process execution over time. Based on the Gantt chart, he calculates the Completion Time (CT) for each process. Subsequently, he computes the Turn Around Time (TAT) using the formula TAT = CT - AT and the Waiting Time (WT) using the formula WT = TAT - BT. The session concludes with the calculation of the average Turn Around Time and average Waiting Time for the set of processes, providing a complete performance analysis of the FCFS algorithm.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor introduces the FCFS algorithm. The slide displays the title 'FCFS (FIRST COME FIRST SERVE)' and bullet points stating it is the simplest scheduling algorithm, managed by a FIFO Queue, and is non-preemptive. The instructor explains that the process requesting the CPU first gets it first, using a background image of a queue to illustrate the concept. He underlines key terms like 'simplest' and 'FIFO Queue' on the slide.

  2. 2:00 – 5:00 02:00-05:00

    The instructor sets up a numerical problem. A table appears with columns for P. No, Arrival Time (AT), and Burst Time (BT). The processes are P0 (AT=2, BT=4), P1 (AT=1, BT=2), P2 (AT=0, BT=3), P3 (AT=4, BT=2), and P4 (AT=3, BT=1). He identifies P2 as the first process because it has the earliest arrival time (0). He draws a Gantt chart, placing P2 from time 0 to 3. He then places P1 (arrived at 1) from 3 to 5, followed by P0 (arrived at 2) from 5 to 9, P4 (arrived at 3) from 9 to 10, and finally P3 (arrived at 4) from 10 to 12. He writes the process names and time intervals on the Gantt chart.

  3. 5:00 – 10:00 05:00-10:00

    The instructor meticulously fills the table with calculated values. For process P2, he calculates Completion Time (CT) as 3, Turn Around Time (TAT) as 3-0=3, and Waiting Time (WT) as 3-3=0. For P1, CT is 5, TAT is 5-1=4, and WT is 4-2=2. For P0, CT is 9, TAT is 9-2=7, and WT is 7-4=3. For P4, CT is 10, TAT is 10-3=7, and WT is 7-1=6. For P3, CT is 12, TAT is 12-4=8, and WT is 8-2=6. He then calculates the averages: Average TAT is (3+4+7+7+8)/5 = 5.8, and Average WT is (0+2+3+6+6)/5 = 3.4. He writes these final calculations at the bottom of the table, showing the summation and division steps.

  4. 10:00 – 10:04 10:00-10:04

    The video concludes with a final view of the completed table and Gantt chart, summarizing the entire solution process for the FCFS scheduling problem. The instructor stands next to the screen, indicating the end of the numerical example.

The lecture provides a clear progression from theoretical definition to practical application. It establishes FCFS as a non-preemptive, FIFO-based algorithm and then immediately demonstrates its execution logic through a step-by-step numerical example. By manually constructing the Gantt chart and deriving performance metrics like Turn Around Time and Waiting Time, the instructor illustrates how arrival times dictate the execution order and how these factors impact overall system efficiency. The final calculation of averages offers a quantitative measure of the algorithm's performance for the given set of processes.

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