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Concept Breakdowns

Process Scheduling Algorithms CPU Burst Comparison

CPU scheduling algorithms determine how an OS allocates processor time to competing processes. Mastering FCFS, SJF, Round Robin, and Priority scheduling — their trade-offs in waiting time, turnaround time, and starvation risk — is essential for OS exams, GATE CS, and systems programming courses.

Interactive Deck

5 Cards
1
Front

What does FCFS scheduling stand for?

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1
Back

First-Come, First-Served: processes execute in arrival order. Simple but causes the convoy effect — short jobs wait behind long ones.

2
Front

Shortest Job First (SJF)

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2
Back

SJF selects the process with the smallest next CPU burst.

  • Optimal average waiting time
  • Requires knowing burst time in advance
  • Risk: starvation of long processes
3
Front

Round Robin time quantum trade-off

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3
Back

Smaller quantum → more context switches, higher overhead. Larger quantum → approaches FCFS behavior. Ideal quantum: 80% of CPU bursts should be shorter than it.

4
Locked

What is preemptive vs non-preemptive scheduling?

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Locked

Priority scheduling starvation fix

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Frequently Asked Questions

What is the difference between SJF and SRTF?

SJF (Shortest Job First) is non-preemptive — the current process runs to completion. SRTF (Shortest Remaining Time First) is preemptive — a new arrival with a shorter burst can interrupt the running process.

  • SJF: lower context switch overhead
  • SRTF: better average waiting time

Why does Round Robin perform poorly with large time quanta?

With a large time quantum, Round Robin degrades toward FCFS behavior — each process runs for a long time before yielding. This increases average waiting time and reduces responsiveness for interactive processes.

How is CPU scheduling tested on GATE CS?

GATE CS frequently asks you to calculate average waiting time and turnaround time for a given arrival/burst time table using FCFS, SJF, Round Robin, or Priority. Practice Gantt chart construction and the formulas: Turnaround Time = Completion − Arrival, Waiting Time = Turnaround − Burst.