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Questions and Answers
What is the main purpose of a scheduler in an operating system?
Which type of scheduler determines the degree of multiprogramming and balances I/O-bound and CPU-bound processes?
What happens to a process after it has either completed or aborted in the ready queue?
Which scheduler is responsible for swapping processes between main memory and disk?
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What role does the dispatcher play in the execution of processes in a queue?
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Which component of the operating system makes decisions on which process to execute next?
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What is the primary goal of the types of schedulers in an operating system?
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Which scheduler optimizes system performance by balancing I/O-bound and CPU-bound processes?
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In what state does a process exist after it has been interrupted and transferred to the waiting queue?
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What does a Long-term Scheduler focus on when selecting processes to bring into the ready queue?
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Study Notes
Process Scheduling
- Process scheduling is a function of the operating system that handles the removal of a running process from the CPU and selects another process to execute based on a particular strategy.
Categories of Scheduling
- Non-preemptive: The resource cannot be taken from a process until the process completes execution.
- Preemptive: The OS allocates resources to a process for a fixed amount of time, and the process switches from running state to ready state or from waiting state to ready state.
Process Scheduling Queues
- Job Queue: Keeps all the processes in the system.
- Ready Queue: Keeps a set of all processes residing in main memory, ready and waiting to execute.
- Device Queues: Keeps processes blocked due to unavailability of an I/O device.
Two-State Process Model
- Running: A new process enters the system in the running state.
- Not Running: Processes not running are kept in a queue, waiting for their turn to execute.
Schedulers
- Long-term Scheduler (Job Scheduler): Selects which processes should be brought into the ready queue, determines the degree of multiprogramming, and optimizes system performance.
- Short-term Scheduler (CPU Scheduler): Decides which process to execute next, invoked frequently (e.g., after every clock interrupt).
- Medium-term Scheduler: Acts as a bridge between long-term and short-term schedulers, controlling the degree of multiprogramming by swapping processes between main memory and disk.
Scheduling Algorithms
- Shortest Job Next (SJN) or Shortest Job First (SJF): A non-preemptive algorithm that assigns priority to processes based on their duration or resource requirements.
- Shortest Remaining Time (SRT): The preemptive version of SJN, allocating the processor to the job closest to completion.
- Round Robin Scheduling: A preemptive algorithm that provides each process a fixed time to execute (called a quantum).
- Multiple-Level Queues Scheduling: Uses other existing algorithms to group and schedule jobs with common characteristics.
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Description
Test your knowledge on Shortest Job Next (SJN) or Shortest Job First (SJF) priority scheduling, a non-preemptive algorithm commonly used in batch systems. Understand how processes are executed based on priority levels and resource requirements.
