Operating Systems CPU Scheduling Quiz

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Questions and Answers

Which of the following is NOT a key characteristic of preemptive scheduling?

It can be essential for real-time applications.

Processes are assigned priorities.

Higher priority tasks can interrupt lower priority tasks.

Tasks always run until completion before releasing the CPU. (correct)

What is the main goal of CPU scheduling?

Optimizing CPU utilization by efficiently managing processes in the ready queue. (correct)

Running all processes simultaneously.

Ensuring that all processes are completed in a fixed order.

Prioritizing processes based on their importance to the user.

Under what condition is a scheduling algorithm considered non-preemptive?

When a process finishes execution and terminates. (correct)

When a process switches from waiting to ready state.

Which type of scheduler is responsible for selecting processes from the ready queue to run on the CPU?

Short-term scheduler/Process scheduler. Signup and view all the answers

What is the primary responsibility of the long-term scheduler?

Determining the order in which processes are loaded into main memory. Signup and view all the answers

Which of the following scheduling algorithms is considered preemptive?

Priority Scheduling. Signup and view all the answers

What is a deadlock situation in the context of operating systems?

When two or more processes are waiting for each other to complete their tasks. Signup and view all the answers

What is the main advantage of using a non-preemptive scheduling algorithm?

It reduces the overhead associated with context switching. Signup and view all the answers

What is a primary disadvantage of the throughput improvement in process scheduling?

The time taken by a process must be known beforehand. Signup and view all the answers

Which scheduling algorithm is most effective when incoming processes are primarily short and execution order is not essential?

First-Come, First-Served (FCFS) Signup and view all the answers

In Multiple-Level Queues Scheduling, what determines which queue a process is assigned to?

A specific property of the process like priority or memory size. Signup and view all the answers

What is a characteristic of Round Robin scheduling?

It provides equal time quantum for each process. Signup and view all the answers

Why is Priority-Based Scheduling effective in mixed process environments?

Kernel-based processes usually have higher priority over user processes. Signup and view all the answers

What occurs during a deadlock situation?

Processes are blocked and waiting for resources held by others. Signup and view all the answers

How can starvation occur in process scheduling?

Longer processes are executed before shorter ones indefinitely. Signup and view all the answers

Which statement about Multiple-Level Queues Scheduling is incorrect?

It can function independently of other scheduling algorithms. Signup and view all the answers

Which of the following scheduling criteria is NOT typically used in process scheduling?

Resource availability Signup and view all the answers

Which of the following conditions is NOT necessary for a deadlock to occur?

Preemption Signup and view all the answers

Which of the following scheduling algorithms prioritizes processes based on their arrival time?

First-Come, First-Served (FCFS) Signup and view all the answers

What does the 'Hold and Wait' condition state in the context of deadlocks?

A process can hold onto a resource while waiting for another. Signup and view all the answers

Which of the following deadlock prevention techniques involves violating the 'Circular Wait' condition?

Resource Ordering Signup and view all the answers

In the 'Ignoring Deadlock' approach to handling deadlocks, what does the operating system assume?

Deadlock will never occur. Signup and view all the answers

The 'Circular Wait' condition refers to:

A chain of processes where each process is waiting for a resource held by the next process in the chain. Signup and view all the answers

Study Notes

CPU Scheduling and Scheduling

CPU scheduling is the process of determining which process will own the CPU for execution while another process is held.
The main task of CPU scheduling is to ensure that whenever the CPU is idle, the operating system (OS) selects at least one of the processes available in the ready queue for execution.
This selection is carried out by the CPU scheduler.
It chooses one of the processes in memory that are ready for execution.

Types of CPU Scheduling

Preemptive Scheduling: Tasks are assigned priorities. A higher priority task might interrupt a lower priority task, even if the lower priority task was already running. The lower priority task resumes when the higher priority task completes.
Non-preemptive Scheduling: The CPU is allocated to a specific process. The process remains in control of the CPU until it releases it, either by switching context or terminating. This method doesn't require special hardware like a timer.

When Scheduling is Preemptive or Non-Preemptive

If only conditions 1 (process switches from running to waiting) and 4 (process finishes execution) apply, the scheduling is non-preemptive.
All other conditions indicate preemptive scheduling.

Scheduler

The scheduler chooses which process runs next when multiple processes are in the ready queue.
A process can move between various scheduling queues throughout its lifetime.
The scheduler selects processes from these queues.
There are three types of schedulers based on the scheduling queue and operating system.
- Long-term scheduler (Job scheduler)
- Medium-term scheduler
- Short-term scheduler (Process scheduler)

Swapping

Swapping is the process of swapping processes in and out of main memory.
Swap-out: When main memory is limited, processes are moved to secondary storage (e.g., hard disk).
Swap-in: A process is loaded back into main memory.

Operations on Processes

Process Creation: New processes can be created by a running process via a system call. The creating process is the parent, and the new processes are children.
Process Resources: Subprocesses can either receive resources directly from the parent or share resources with the parent process.
Process Execution: Parent and child processes can execute concurrently or the parent can wait for its children to terminate. Parent and child processes can share or have separate address spaces.
Process Identification: Each process is identified by a unique process identifier (PID).
Process Creation: A new process is created using the fork system call.
Process Communication: Processes sharing an address space can communicate directly.

Process Termination

Process termination occurs when a process finishes its execution. This can be normal or abnormal termination, with the OS potentially initiating the termination.
Resources held by the terminated process are deallocated.
Child processes might return data to the parent process.
A parent process might terminate its children due to tasks no longer required or if an error occurs.

CPU Scheduling Terminologies

Burst Time/Execution Time: Time required for process execution. Often referred to as CPU bursts.
Arrival Time: When a process enters the ready state.
Finish Time: When a process completes and leaves the system.
Multiprogramming: Multiple programs residing in memory at the same time.
Jobs: Programs without user interaction.
Users: Programs with user interaction.
Process: The basis of all job and user programs.
CPU/IO Burst Cycle: The process alternates between CPU execution and I/O operations. CPU bursts are typically shorter than I/O.

CPU Scheduling Criteria

Maximize:
- CPU Utilization: Keeping the CPU busy as much as possible in the system.
- Throughput: The number of processes completed per unit of time.
Minimize:
- Waiting Time: The time a process waits in the ready queue.
- Response Time: The time it takes for a process to respond to a request.
- Turnaround Time: The total time a process spends in the system from submission to completion.

Interval Timer

An interval timer is closely related to preemption.
A process receives allocated CPU time, and a timer is set for a specific interval.
This timer interrupt and process preemption force the processes to return the CPU before the burst completes.
This prevents processes from monopolizing the system resources.

Types of CPU Scheduling Algorithms

First Come First Serve (FCFS): Processes are executed in the order they arrive. Simple to implement but can lead to longer wait times for shorter processes.
Shortest Job First (SJF): Processes with the shortest execution time are given priority. Improves efficiency but requires knowing the process's execution time in advance.
Shortest Remaining Time (SRT): A preemptive version of SJF. If a shorter process arrives while a longer process is running, the shorter process preempts the longer process.
Priority Scheduling: Processes are assigned priorities, with higher priority processes being executed first. Requires a method assigning priorities.
Round Robin: Processes are executed in a circular fashion, with each process getting a time slice. Each process is given a slot, thus preventing starvation.
Multilevel Queue Scheduling: Processes are sorted into various queues based on characteristics (priority, memory size, etc.). Separate scheduling algorithms can operate on each queue.

Deadlocks

A set of processes are blocked, each holding a resource and waiting for another resource held by a blocked process.

Methods of Handling Deadlocks

Ignoring the Deadlock: The OS assumes deadlocks won't occur, which is practical in many OS functions involving many users.
Deadlock Prevention: Prevents the occurrence of one or more deadlock conditions (Mutual Exclusion, Hold and Wait, No Preemption, Circular Wait).
Deadlock Avoidance: Uses algorithms to ensure the system remains in a safe state at all times, avoiding deadlocks.
Deadlock Detection and Recovery: Detects deadlocks when they arise and recovers the system by preempting resources or terminating processes.

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Description

Test your knowledge of CPU scheduling in operating systems with this quiz. It covers key characteristics of preemptive and non-preemptive scheduling, scheduling algorithms, and roles of different types of schedulers. Perfect for students studying operating system concepts.