Pre-emptive Priority Scheduling

Duration: 6 min

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AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This educational video explains the Pre-emptive Priority Scheduling algorithm in Operating Systems. The lecturer defines the concept where a higher priority process interrupts a running lower priority process, causing a context switch. He then solves a numerical problem involving six processes (P0-P5) with specific Arrival Times, Burst Times, and Priorities. The solution involves constructing a Gantt chart to determine execution order and calculating Completion Time (CT), Turnaround Time (TAT), and Waiting Time (WT) for each process.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The lecturer introduces the concept of Priority Scheduling, specifically the pre-emptive variant. He explains that once a decision is made, the process with the highest priority is scheduled on the CPU. Crucially, he notes that if a new process enters the system with a priority higher than the currently running process, a context switch occurs, and the processor is immediately provided to the new high-priority process. This establishes the core mechanism of pre-emption where higher priority tasks interrupt lower priority ones.

  2. 2:00 – 5:00 02:00-05:00

    The lecture transitions to a numerical problem involving six processes: P0 through P5. A table is displayed showing Arrival Time (AT), Burst Time (BT), and Priority for each. The lecturer begins constructing a Gantt chart to visualize the execution order. He analyzes the arrival times, noting P0 arrives at time 1, while P1 and P2 arrive at time 2. He identifies P3 as having the highest priority (8), marked as 'H' on the board. He starts drawing the timeline, marking the initial idle period and the entry of processes, preparing to determine which process runs next based on the priority rules.

  3. 5:00 – 6:30 05:00-06:30

    The lecturer completes the Gantt chart and fills in the calculation table. He determines the Completion Time (CT) for each process based on the execution order derived from the Gantt chart. For instance, P3 completes at time 8. He then calculates Turnaround Time (TAT) using the formula TAT = CT - AT and Waiting Time (WT) using WT = TAT - BT. He fills the columns with specific values, such as P0 having a CT of 18 and a WT of 13, while P3 has a WT of 0. The video concludes with the table fully populated, ready for the final average calculation.

The video provides a comprehensive guide to Pre-emptive Priority Scheduling. It starts with the theoretical definition, emphasizing the context switch mechanism when higher priority processes arrive. It then applies this theory to a concrete example, demonstrating how to manage multiple processes with varying arrival and burst times. The step-by-step construction of the Gantt chart and the subsequent calculation of performance metrics like TAT and WT offer a clear method for solving such operating system problems.

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