chapter
    CPU Scheduling Short Notes for GATE CS

    CPU Scheduling short notes for GATE CS: 6 study cards covering concepts, formulas, shortcuts and exam traps, plus solved practice questions.

    cpu scheduling short notes

    The Ultimate SRTF Execution Checklist

    1
    Initialize Table: PID, AT, BT, RBT (copy of BT), CT.
    2
    Start Clock: . If no arrival, jump to min .
    3
    Filter Ready Queue: and .
    4
    Select Winner: Min . Tie? Min .
    5
    Execute: Run 1 unit. . .
    6
    Check Completion: If , set .
    7
    Loop: Repeat until all recorded.
    8
    Calculate: , .

    The Ultimate Algorithm Cheat Sheet

    Final Rapid-Fire Recall

    FCFS
    Non-preemptive | Convoy Effect | No Starvation
    SJF / SRTF
    Optimal Waiting Time | Starvation Possible | No Convoy Effect
    Priority
    Starvation Possible | Solved by Aging
    Round Robin
    Preemptive | No Starvation | High Context Switch Overhead (if quantum is small)

    The Ultimate Round Robin Checklist

    The Ultimate Round Robin Checklist

    • Queue Discipline: Strictly FIFO. Preempted processes go to the tail.
    • Preemption Rule: Happens exactly at multiples of . Never in the middle of a quantum.
    • Termination at Boundary: If burst ends exactly at , it terminates. It does not re-enter the queue.
    • Context Switch Count: Total Blocks in Gantt .
    • New Arrivals: Enter the queue before the preempted process is added to the tail.
    • Starvation: Impossible in pure Round Robin.

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    CPU Scheduling Short Notes for GATE CS

    CPU Scheduling short notes for GATE CS: 6 study cards covering concepts, formulas, shortcuts and exam traps, plus solved practice questions.

    The Ultimate SRTF Execution Checklist

    1
    Initialize Table: PID, AT, BT, RBT (copy of BT), CT.
    2
    Start Clock: . If no arrival, jump to min .
    3
    Filter Ready Queue: and .
    4
    Select Winner: Min . Tie? Min .
    5
    Execute: Run 1 unit. . .
    6
    Check Completion: If , set .
    7
    Loop: Repeat until all recorded.
    8
    Calculate: , .

    The Ultimate Algorithm Cheat Sheet

    Final Rapid-Fire Recall

    FCFS
    Non-preemptive | Convoy Effect | No Starvation
    SJF / SRTF
    Optimal Waiting Time | Starvation Possible | No Convoy Effect
    Priority
    Starvation Possible | Solved by Aging
    Round Robin
    Preemptive | No Starvation | High Context Switch Overhead (if quantum is small)

    The Ultimate Round Robin Checklist

    The Ultimate Round Robin Checklist

    • Queue Discipline: Strictly FIFO. Preempted processes go to the tail.
    • Preemption Rule: Happens exactly at multiples of . Never in the middle of a quantum.
    • Termination at Boundary: If burst ends exactly at , it terminates. It does not re-enter the queue.
    • Context Switch Count: Total Blocks in Gantt .
    • New Arrivals: Enter the queue before the preempted process is added to the tail.
    • Starvation: Impossible in pure Round Robin.

    Final Exam Readiness: If You See X, Do Y

    Final Exam Readiness: If You See X, Do Y

    Pattern 1: "Find the average waiting time"

    Draw the Gantt chart. Calculate Completion Time for each. Apply . Do not forget to include context switch time in the CT if .

    Pattern 2: "How many context switches occurred?"

    Draw the Gantt chart. Count the total number of process blocks. Subtract 1.

    Pattern 3: "Process A switched to B exactly twice..."

    This is a reverse-engineering puzzle. Map the transitions to Gantt blocks. Use the queue logic to determine the order. Use the quantum to bound the burst times.

    Pattern 4: "What happens if quantum is increased to infinity?"

    The answer is always "It becomes FCFS" or "Waiting time increases and response time degrades".

    Pattern 5: "Which algorithm is best for interactive systems?"

    Round Robin. Keyword match: Interactive equals good response time equals Round Robin.

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