CPU Scheduling Algorithms Overview

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Questions and Answers

What is the primary function of the memory management component of an operating system?

To allocate and deallocate memory for running programs. (correct)

To manage the CPU status and allocate processor time.

To handle user interface interactions with hardware.

To control input and output device operations.

In which scenario does an operating system utilize memory management techniques?

When hardware components need to be updated or replaced.

When a user opens multiple applications at the same time. (correct)

When a software program seeks to access network resources.

When the CPU prioritizes a specific process for execution.

Which of the following is NOT a task performed by the operating system in terms of processor management?

Allocating and deallocating processor time to processes.

Determining the status of the processor and processes.

Selecting which process receives CPU time.

Keeping a record of the current memory usage. (correct)

How does an operating system handle multiple processes running simultaneously?

By determining the order and timing of CPU allocation. Signup and view all the answers

What role does the operating system play in multiprocessing?

It selects which processes will have access to memory resources. Signup and view all the answers

What would happen if the operating system did not manage memory effectively?

Programs may fail to run due to insufficient memory allocation. Signup and view all the answers

Which component of an operating system is responsible for recording the status of active processes?

Process scheduler. Signup and view all the answers

What typically occurs when a program completes execution in terms of memory management?

The program's memory region is released for future use. Signup and view all the answers

What is the primary goal of CPU utilization in an operating system?

To keep the CPU as busy as possible Signup and view all the answers

Which of the following accurately defines throughput in the context of CPU scheduling?

The number of processes that finish execution per unit time Signup and view all the answers

Which term describes the time from process submission until completion?

Turnaround time Signup and view all the answers

In which CPU scheduling algorithm does the process requesting the CPU first get prioritized?

First Come First Serve Signup and view all the answers

What best describes waiting time in CPU scheduling?

Time spent in the ready queue before execution Signup and view all the answers

What is a characteristic of Priority Scheduling in CPU algorithms?

Higher priority processes are executed before lower priority ones Signup and view all the answers

Which of the following is not a type of CPU scheduling algorithm?

First Come Last Serve (FCLS) Signup and view all the answers

What is the importance of minimizing response time in CPU scheduling?

To ensure user requests are addressed quickly Signup and view all the answers

What is the primary function of a medium term scheduler?

To remove processes from memory and reduce multiprogramming Signup and view all the answers

What does the dispatcher do after the short-term scheduler selects a process?

Transfers the selected process to the CPU for execution Signup and view all the answers

Which of the following best describes the relationship between the scheduler and the dispatcher?

The scheduler selects a process while the dispatcher executes it Signup and view all the answers

Which action is NOT performed by the dispatcher during its function?

Implementing the scheduling algorithm Signup and view all the answers

What is the term used for moving a process out of memory by the medium term scheduler?

Swapping Signup and view all the answers

During CPU scheduling, what does the operating system consider when selecting a process?

The priority level of the processes waiting in the ready queue Signup and view all the answers

What process occurs after a process is selected by the scheduler?

The process is placed into the running state by the dispatcher Signup and view all the answers

Which of the following statements about CPU scheduling is true?

CPU scheduling determines which process will run while others are waiting Signup and view all the answers

What is the formula for calculating Turn Around Time (TAT)?

Completion time - Arrival time Signup and view all the answers

In a round-robin scheduling algorithm with a time quantum of 4 milliseconds, what happens when a process does not complete within the time quantum?

The process is preempted and moved to the end of the queue. Signup and view all the answers

How is waiting time calculated?

TAT - Burst time Signup and view all the answers

What is the average waiting time when the total waiting time is 17 milliseconds across 3 processes?

5.66 milliseconds Signup and view all the answers

What differentiates foreground processes from background processes?

Foreground processes are interactive, while background processes are batch processes. Signup and view all the answers

Which scheduling method is commonly used for separating processes into groups based on response times?

Multilevel Queue Scheduling Signup and view all the answers

What role does a time quantum play in Round Robin scheduling?

It dictates how long a process is allowed to execute before being preempted. Signup and view all the answers

Which of the following is NOT a characteristic of background processes?

They operate interactively with user input. Signup and view all the answers

What is the primary characteristic of Asymmetric Multiprocessing?

A single processor handles scheduling and I/O processing. Signup and view all the answers

In Symmetric Multiprocessing, how do processors manage process scheduling?

Each processor has its own private queue. Signup and view all the answers

What effect does Processor Affinity have on cache memory when a process migrates to another processor?

The cache must be invalidated and repopulated. Signup and view all the answers

What is Soft Affinity in the context of process scheduling?

The OS attempts to keep a process on the same processor but does not guarantee it. Signup and view all the answers

Which statement accurately describes Hard Affinity?

It permits a process to specify a subset of processors on which it may run. Signup and view all the answers

Why do most Symmetric Multiprocessing systems try to avoid process migration?

Migration can lead to performance degradation due to cache invalidation. Signup and view all the answers

Which of the following best defines the role of the Master Server in Asymmetric Multiprocessing?

To handle all scheduling decisions and I/O processing. Signup and view all the answers

What happens to the cache memory when a process with soft affinity is reallocated to another processor?

The cache for the first processor is invalidated while the second is populated. Signup and view all the answers

Study Notes

Scheduling Criteria

CPU utilization is crucial for operating systems, aiming for maximum CPU usage between 0-100%.
Real-time operating systems (RTOS) target CPU utilization of 40% for low-level and 90% for high-level systems.
Throughput refers to the number of processes completed per unit of time while the CPU executes tasks.

Minimizing Times

Waiting time refers to the duration a process remains in the ready queue before execution.
Response time is the interval from request submission to the generation of the first response.
Turnaround time (TAT) is the total time taken from process submission to completion, including wait time and execution time.

Types of CPU Scheduling Algorithms

First Come First Serve (FCFS)
Shortest-Job-First (SJF) Scheduling
Shortest Remaining Time
Priority Scheduling
Round Robin Scheduling
Multilevel Queue Scheduling

First Come First Serve (FCFS)

FCFS is the simplest CPU scheduling algorithm where the first process to request CPU gets allocated first.
Managed using a First-In-First-Out (FIFO) queue.

Functions of Operating System (OS)

Acts as an interface between hardware and user while managing software-hardware interactions.
Handles essential functions like memory management, process scheduling, and resource allocation.

Memory Management

Manages primary memory, which must be accessible by the CPU for executing programs.
Allocates and deallocates memory for processes, records memory usage, and manages distribution during multiprogramming.

Processor Management/Scheduling

Manages CPU processes and determines when each process will use the CPU.
Allocates/deallocates CPU resources and keeps track of CPU status.

Medium Term Scheduler

Temporarily removes processes from memory to reduce multiprogramming.
Swaps processes in and out of memory to continue execution.

Dispatcher

A program that transfers control of the CPU to the selected process after scheduling is done.
Involves context switching, switching to user mode, and jumping to the process's instruction point.

Difference Between Scheduler and Dispatcher

The scheduler selects a process from the ready queue for execution.
The dispatcher takes the selected process and transitions it to the running state.

CPU Scheduling

Determines which process will execute on the CPU while others are on hold.
Sets a timer for interruptions to manage process execution.

Turnaround Time and Waiting Time Formulas

Turnaround time (TAT) = Completion time - Arrival time
Waiting time = TAT - Burst time (BT)
Alternatively, TAT = Burst time + Waiting time.

Round Robin Scheduling (RR)

If the time quantum is set to 4 milliseconds, processes take turns utilizing the CPU.
Each process receives a time slice before the next process in the queue is executed.

Multilevel Queue Scheduling

Different processes use different scheduling algorithms based on type (interactive vs. background).
Background processes generally take priority over interactive processes.

Approaches to Multiple-Processor Scheduling

Asymmetric Multiprocessing: A master processor manages all scheduling and I/O; other processors execute user code.
Symmetric Multiprocessing: Each processor self-schedules, with possible shared or private ready queues.

Processor Affinity

Refers to a process's tendency to run on a specific processor, promoting cache memory efficiency.
Reduces the need for cache invalidation when processes migrate between processors.

Types of Processor Affinity

Soft Affinity: Attempts to keep a process on the same processor without strict guarantees.
Hard Affinity: Allows processes to define specific processors on which they may run, supported in certain systems like Linux.

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Description

This quiz explores key concepts related to CPU scheduling algorithms used in operating systems. It covers important criteria such as CPU utilization, waiting time, response time, and different types of scheduling methods like FCFS, SJF, and Round Robin. Test your understanding of how these factors impact overall system performance.