Scheduling

• What is the purpose of scheduling in multitasking operating systems?

  To manage which processes to execute next and the length of time each process can execute
• How do multitasking operating systems give the appearance of multiple tasks executing simultaneously?

  By managing multiple threads that may need to be executed at once
• In a multi-user environment, what is required for seamless servicing of multiple users?

  Operating systems need a scheduler
• What is the ready queue in process scheduling?

  A queue where processes wait to be executed by the CPU
• How does the First Come First Serve scheduling algorithm work?


  Processes are executed strictly in the order they arrive
• What is a drawback of the First Come First Serve scheduling algorithm?

  Long processes can cause others to wait unnecessarily
• How does the Shortest Job First scheduling algorithm operate?

  It picks the process that takes the shortest amount of time to execute
• What is the time slice in a Round Robin scheduling algorithm?

  A fixed amount of time allocated to each process
• What happens to a process in Round Robin scheduling if it is not complete by the end of its time slice?

  It returns to the back of the ready queue
• What is the difference between Shortest Job First and Shortest Remaining Time scheduling algorithms?

  Shortest Remaining Time is preemptive, allowing a process to be suspended if a higher priority process arrives
• What is the purpose of Multi-Level Feedback Queues in scheduling?

  To separate processes into multiple queues based on their need for the processor
• How does a process get promoted or demoted in a Multi-Level Feedback Queue?

  Processes are moved based on their CPU time usage and input/output needs
• What are the five scheduling algorithms to be aware of for the exam?

  • First Come First Serve (FCFS)
  • Shortest Job First (SJF)
  • Shortest Remaining Time (SRT)
  • Round Robin (RR)
  • Multi-Level Feedback Queues (MLFQ)
• What are the key characteristics of the First Come First Serve scheduling algorithm?

  • Processes are executed in the order they arrive
  • No preemption occurs
  • Can lead to long wait times for shorter processes
• What are the key characteristics of the Shortest Job First scheduling algorithm?

  • Executes the process with the shortest execution time first
  • Non-preemptive
  • Requires knowledge of process durations
• What are the key characteristics of the Round Robin scheduling algorithm?

  • Each process is given a fixed time slice
  • Preemptive
  • Fairly distributes CPU time among processes
• What are the key characteristics of the Shortest Remaining Time scheduling algorithm?

  • Preemptive version of Shortest Job First
  • Allows a process to be suspended if a higher priority process arrives
  • Requires knowledge of remaining process durations
• What are the key characteristics of Multi-Level Feedback Queues?


  • Separates processes into multiple queues based on CPU and I/O needs
  • Allows processes to be promoted or demoted between queues
  • Can use different scheduling algorithms for different queues