Podcast
Questions and Answers
In the Shortest-Job-First (SJF) scheduling example, what is the waiting time for process P2?
In the Shortest-Job-First (SJF) scheduling example, what is the waiting time for process P2?
In the Shortest-Remaining-Time-First (SRTF) example, which process is executed first?
In the Shortest-Remaining-Time-First (SRTF) example, which process is executed first?
What is the main difference between SJF and SRTF scheduling algorithms?
What is the main difference between SJF and SRTF scheduling algorithms?
In priority scheduling, how are equal-priority processes handled?
In priority scheduling, how are equal-priority processes handled?
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Which of the following statements about priority scheduling is true?
Which of the following statements about priority scheduling is true?
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In the provided example of preemptive SJF scheduling, what is the waiting time for process P3?
In the provided example of preemptive SJF scheduling, what is the waiting time for process P3?
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What is the relationship between the SJF algorithm and the priority scheduling algorithm?
What is the relationship between the SJF algorithm and the priority scheduling algorithm?
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In preemptive priority scheduling, what happens when a new process arrives with a higher priority than the currently running process?
In preemptive priority scheduling, what happens when a new process arrives with a higher priority than the currently running process?
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In non-preemptive priority scheduling, what happens when a new process arrives with a higher priority than the currently running process?
In non-preemptive priority scheduling, what happens when a new process arrives with a higher priority than the currently running process?
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In the SJF scheduling example, what is the average waiting time for the four processes?
In the SJF scheduling example, what is the average waiting time for the four processes?
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Study Notes
Scheduling Algorithms
- Shortest-Job-First (SJF) scheduling algorithm: executes the process with the shortest burst time first.
- SJF scheduling chart: shows the sequence of processes executed, and the average waiting time can be calculated.
- Average waiting time = (sum of waiting times of all processes) / number of processes.
Shortest-Remaining-Time-First (SRTF)
- Preemptive version of SJF: the process with the shortest remaining time is executed first.
- SRTF Gantt Chart: shows the sequence of processes executed, and the average waiting time can be calculated.
- Average waiting time = (sum of waiting times of all processes) / number of processes.
Priority Scheduling
- Priority scheduling algorithm: assigns a priority to each process, and the CPU is allocated to the process with the highest priority.
- Equal-priority processes are scheduled in FCFS (First-Come-First-Served) order.
- Priority scheduling can be either preemptive or non-preemptive.
Scheduling Queues
- Scheduling queues: a queueing diagram represents the process scheduling, with rectangular boxes representing queues and circles representing resources.
- Ready queue: holds processes waiting for the CPU.
- Device queues: hold processes waiting for I/O devices.
- New process is initially put in the ready queue, then may switch to the waiting state and back to the ready queue.
Schedulers
- Long-term scheduler (or job scheduler): selects processes from the pool and loads them into memory for execution.
- Short-term scheduler (or CPU scheduler): selects which process should be executed next and allocates the CPU.
- Long-term scheduler controls the degree of multiprogramming.
Process Types
- I/O-bound process: spends more time doing I/O than computations.
- CPU-bound process: spends more time doing computations.
- Long-term scheduler selects a good process mix of I/O-bound and CPU-bound processes.
Medium-Term Scheduler
- Medium-term scheduler: removes a process from memory to reduce the degree of multiprogramming.
- Swapping: the process is swapped out and later swapped in, allowing the process to continue execution.
Context Switch
- Context switch: when the CPU switches to another process, the context of the current process is saved, and the context of the new process is loaded.
- Context is represented in the PCB (Process Control Block) of the process.
Process Termination
- Process termination: when a process finishes executing and asks the operating system to delete it using the exit() system call.
- Resources of the process are deallocated by the operating system.
- A process can cause the termination of another process via an appropriate system call.
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Description
Learn about process scheduling and queues in operating systems through a queueing diagram representation. Understand the concept of ready queues, device queues, and the flow of processes within the system.
