Round Robin_Practice
Duration: 7 min
This video lesson is available to enrolled students.
AI Summary
An AI-generated summary of this video lecture.
The video provides a comprehensive tutorial on the Round Robin scheduling algorithm, a critical topic in operating systems for time-sharing systems. The lecture begins with a slide defining Round Robin as an algorithm where the ready queue is treated as a circular queue (FIFO) and pre-emption is used to switch between processes. The instructor explains that the CPU scheduler allocates the CPU to each process for a time interval equivalent to 1 Time quantum (TQ). He sets a specific Time Quantum (Q) of 3 for the numerical example. The problem involves six processes (P0 to P5) with varying Arrival Times (AT) and Burst Times (BT). The instructor systematically works through the problem, first organizing the data by circling the AT and BT columns. He then constructs a Gantt chart by hand, writing the execution sequence of processes on the screen. He calculates the Completion Time (CT) for each process, determining when each one finishes. Finally, he computes the Turn Around Time (TAT) and Waiting Time (WT) using the formulas TAT = CT - AT and WT = TAT - BT, and concludes by calculating the average TAT and average WT for the entire set of processes. This detailed walkthrough helps students understand the mechanics of Round Robin and how to evaluate its performance metrics.
Chapters
0:00 – 2:00 00:00-02:00
The video opens with a slide titled "Round robin" which defines the algorithm for time-sharing systems. The text explains that the ready queue is treated as a circular queue (FIFO) and that pre-emption allows switching between processes. The instructor writes "Q = 3" on the screen, setting the time quantum. He then focuses on a table with six processes (P0 to P5). He circles the Arrival Time (AT) column, highlighting values 5, 4, 3, 1, 2, and 6. He also circles the Burst Time (BT) column, highlighting values 5, 6, 7, 9, 2, and 3. He prepares to solve the problem by organizing this data.
2:00 – 5:00 02:00-05:00
The instructor begins solving the problem by writing the execution sequence on the screen, effectively creating a Gantt chart. He writes the sequence: P3, P4, P2, P1, P3, P0, P5, P2, P1, P3, P0, P2. He marks the time points along the bottom: 0, 1, 4, 6, 9, 12, 15, 18, 21, 24, 27, 30, 32. He tracks the remaining burst time for each process, writing reduced values next to the original burst times, such as writing "2" next to P0's burst time of 5. He determines the Completion Time (CT) for each process, circling values like 32 for P0, 27 for P1, 24 for P2, 15 for P3, 6 for P4, and 18 for P5. He writes these completion times in the "Completion Time (CT)" column of the table.
5:00 – 6:44 05:00-06:44
The instructor fills in the final columns of the table. He calculates Turn Around Time (TAT) and Waiting Time (WT) for each process. For P0, he calculates TAT as 32 - 5 = 27 and WT as 27 - 5 = 22. He repeats this for all processes: P1 (TAT 23, WT 17), P2 (TAT 21, WT 14), P3 (TAT 14, WT 5), P4 (TAT 4, WT 2), and P5 (TAT 12, WT 9). He then calculates the average TAT by summing the values (101) and dividing by 6, resulting in approximately 16.83. He calculates the average WT by summing the values (69) and dividing by 6, resulting in 11.5. He writes these averages in the "Average" row at the bottom of the table.
The video effectively demonstrates the Round Robin scheduling algorithm through a step-by-step numerical example. It transitions from theoretical definitions on a slide to practical application by constructing a Gantt chart and filling out a performance table. The instructor clearly shows how to calculate Completion Time, Turn Around Time, and Waiting Time, culminating in the calculation of average metrics. This progression helps students understand both the mechanics of the algorithm and how to evaluate its performance.