38 Questions
What is the main purpose of scheduling in a system?
To ensure efficient execution of processes and optimal CPU utilization
Which type of scheduling allows the OS to assign resources to a process for a predetermined period?
Preemptive scheduling
What is the function of the Job Queue in a system?
It contains all the processes in the system
What type of scheduler determines which processes are to be admitted into the system?
Long-term Scheduler (Job Scheduler)
Which type of scheduling is used when a process terminates?
Non-Preemptive scheduling
What is the function of the Short-term Scheduler (CPU Scheduler)?
It schedules the processes to be executed next
What is the primary advantage of the First-Come, First-Served scheduling algorithm?
Simple and easy to implement
What is the function of the Medium-term Scheduler?
It manages the swapping of processes in and out of memory
What type of scheduling is used when a process switches from running state to ready state?
Preemptive scheduling
What is the formula to calculate the Turnaround Time of a process?
Turnaround Time = Completion Time - Arrival Time
Which of the following is NOT a characteristic of the Shortest Job Next (SJN) scheduling algorithm?
Executes processes in the order of arrival
What is the Response Time of a process?
Time between process arrival and first execution
What is the term for the moment when a process enters the ready queue and awaits execution by the CPU?
Arrival Time
What is the formula to calculate the Waiting Time of a process?
Waiting Time = Turnaround Time - Burst Time
In the FCFS scheduling algorithm, which process will be executed first?
P1
What is the waiting time for P3?
5
What is the primary purpose of context switching in operating systems?
To switch the CPU from one process to another for smooth execution
Which of the following statements is true about FCFS?
It is a non-preemptive scheduling algorithm
When does context switching happen?
When a high-priority process comes to a ready state
What is the definition of a thread in operating systems?
The smallest unit of a process that can be scheduled and executed by the CPU
What is the burst time for P5?
2
What is an advantage of using threads in operating systems?
Responsiveness and resource sharing
What is the average waiting time for the given processes?
4.8
What type of thread is managed by the operating system kernel?
Kernel-Level Thread (KLT)
In FCFS, which process will be executed last?
P5
What is the state of a thread when it is waiting for resources?
Blocked
What is the arrival time for P4?
6
What is the purpose of calculating the average waiting time?
To evaluate the performance of the scheduling algorithm
What is process scheduling in operating systems?
The method by which the operating system decides which process runs at any given time
Why is creating and managing threads less costly than processes?
Because threads share memory and resources
What is the main characteristic of Non-preemptive SJF scheduling?
Once a process starts, it cannot be interrupted until it finishes.
What is the main advantage of Priority Scheduling?
It minimizes average waiting time.
What is the solution to Starvation in Priority Scheduling?
Aging, which is a technique of gradually increasing the priority of processes that wait in the system for a long time.
What is the main characteristic of Preemptive SJF scheduling?
A running process can be interrupted if a new process with a high priority number arrives.
What is the main disadvantage of Priority Scheduling?
It can lead to starvation of lower priority processes.
What is the main characteristic of Round Robin scheduling?
A process is allocated a fixed time slot and is preempted if it does not finish execution within that time.
What is the main difference between Preemptive SJF and Non-preemptive SJF?
The ability to interrupt a running process.
What is the term for a process running out of resources because other processes are using it?
Starvation
Study Notes
Context Switching
- Involves switching the CPU from one process to another, ensuring smooth execution of multiple processes.
- Happens when a high-priority process comes to a ready state, an interrupt occurs, user and kernel-mode switch, or preemptive CPU scheduling is used.
Threads in Operating Systems
- Definition: The smallest unit of a process that can be scheduled and executed by the CPU.
- Importance: Allows parallelism within a process, leading to more efficient and faster execution.
- Types of Threads:
- User-Level Threads (ULTs): Managed by user-level libraries, with fast context switch and no OS modification required.
- Kernel-Level Threads (KLTs): Managed by the operating system kernel, with the OS managing and scheduling threads independently.
Advantages of Using Threads
- Responsiveness: Allows a program to continue running even if part of it is blocked.
- Resource Sharing: Threads of the same process share memory and resources.
- Economy: Creating and managing threads is less costly than processes.
- Scalability: Threads can run on different processors in a multiprocessor system.
Thread Lifecycle
- New: Thread is created.
- Runnable: Thread is ready to run.
- Running: CPU is executing the thread.
- Blocked: Thread is waiting for resources.
- Terminated: Thread has finished execution.
Process Scheduling in Operating Systems
- Definition: The method by which the operating system decides which process runs at any given time.
- Importance: Ensures efficient execution of processes, optimal CPU utilization, and overall system performance.
Categories of Scheduling
- Non-preemptive: A process's resource cannot be taken before the process has finished running.
- Preemptive: The OS assigns resources to a process for a predetermined period, and the process switches from running state to ready state or from waiting state to ready state during resource allocation.
Types of Schedulers
- Long-term Scheduler (Job Scheduler): Determines which processes are to be admitted into the system and brings the new process to the 'Ready State'.
- Short-term Scheduler (CPU Scheduler): Selects which process should be executed next and brings process from the ready state for scheduling it on the running state.
- Medium-term Scheduler: Manages swapping of processes in and out of memory to balance load.
Scheduling Queues
- Job Queue: All processes in the system.
- Ready Queue: Processes that are ready to run.
- Device Queue: Processes waiting for devices (I/O).
Scheduling Algorithms Overview
- Two types of scheduling methods:
- Preemptive Scheduling: Used when a process switches from running state to ready state or from waiting state to ready state.
- Non-Preemptive Scheduling: Used when a process terminates, or when a process switches from running state to waiting state.
CPU Scheduling Algorithms
- First-Come, First-Served (FCFS): Processes are executed in the order they arrive.
- Shortest Job Next (SJN): Processes are executed in the order of their burst time.
- Priority Scheduling: Processes are assigned priority numbers, and the highest priority process is selected next.
- Round Robin (RR): Each process is allocated a fixed time slot (time quantum), and if a process does not finish execution within its time quantum, it is preempted and placed at the end of the ready queue.
Key Concepts in CPU Scheduling
- Arrival Time: The moment in time when a process enters the ready queue and is awaiting execution by the CPU.
- Burst Time: The amount of CPU time the process requires to complete its execution.
- Completion Time: The summation of the arrival, waiting, and burst times.
- Turnaround Time: The time elapsed between the arrival of a process and its completion.
- Waiting Time: A process's duration in the ready queue before it begins executing.
- Response Time: The duration between the arrival of a process and the first time it runs.
This quiz covers the concept of context switching, which involves switching the CPU from one process to another, ensuring smooth execution of multiple processes.
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