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Advanced Scheduling Algorithms in Operating Systems: FCFS, SJF, Priority, and Round Robin

This resource explores various scheduling criteria and algorithms crucial in operating systems. Key metrics such as CPU utilization, throughput, turnaround time, waiting time, and response time are analyzed. The document details the First-Come-First-Serve (FCFS), Shortest Job First (SJF) methods (both preemptive and non-preemptive), priority scheduling, and round-robin scheduling techniques. Additionally, it covers advanced concepts like multilevel queue and multilevel feedback queue scheduling, emphasizing criteria for process priority, upgrade or downgrade strategies, and efficient queue management.

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Advanced Scheduling Algorithms in Operating Systems: FCFS, SJF, Priority, and Round Robin

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  1. Process Scheduling II(5.3) CPE 261403 - Operating Systems http://www.e-cpe.org/moodle

  2. Scheduling Criteria (5.2) • CPU Utilization • Throughput • Turnaround time • Waiting time • Response time

  3. Scheduling Algorithms (5.3) • FCFS • SJF (non-preemptive / preemptive) • Priority Scheduling • Round-Robin Scheduling • Multilevel Queue Scheduling • Multilevel Feedback-Queue Scheduling

  4. Priority Scheduling • Defining Priorities • Internally Defined Priorities (i.e. Memory requirements, Time to execute) • External priorities (usually defined by the user) (i.e. importance of the process)

  5. Starvation

  6. IBM 7094 at MIT When closing down in 1973, found a process submitted in 1967 (Myth)

  7. Round Robin Scheduling • Preemptive by Nature • Defines a Time Quantum • Time Quantum >> Context Switch Time

  8. Multilevel Queue Scheduling • Scheduling within & among queues • Use simple priority or CPU time slice (quota)

  9. Multilevel Feedback Queue • Example: Q1=RR, Q2=RR, Q3=FCFS

  10. Multilevel Feedback Queue • Parameters: • Number of queues • Scheduling algorithms for each queue • When to upgrade a process (i.e. when it requests I/O) • When to downgrade a process (i.e. when it exceeds the time quantum) • Which queue should a new process enter

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