Operating Systems CPU Scheduling Overview
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Operating Systems CPU Scheduling Overview

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Questions and Answers

What happens when a trap or interrupt occurs in the operating system?

  • The system switches to kernel mode. (correct)
  • The system remains in user mode.
  • The system immediately shuts down.
  • The system executes the instruction as usual.
  • Which of the following is a characteristic of kernel mode?

  • User programs can directly manage I/O controls.
  • Limited access to hardware resources.
  • Execution of privileged instructions is allowed. (correct)
  • The system is restricted from accessing memory.
  • What is the role of system calls in an operating system?

  • To execute user programs in kernel mode.
  • To provide user programs access to the hardware directly.
  • To allow user programs to request services from the operating system. (correct)
  • To interrupt the operating system at any time.
  • What type of instruction is used to switch to kernel mode?

    <p>Privileged instruction.</p> Signup and view all the answers

    How does the hardware handle a privileged instruction executed in user mode?

    <p>It treats the instruction as illegal and traps it.</p> Signup and view all the answers

    In what manner is a system call typically executed by the hardware?

    <p>As a software interrupt.</p> Signup and view all the answers

    What is the purpose of a timer in operating systems?

    <p>To prevent user programs from monopolizing the CPU.</p> Signup and view all the answers

    How does a system call indicate what type of service the user program is requesting?

    <p>Using a parameter associated with the interrupt.</p> Signup and view all the answers

    What is the primary purpose of CPU scheduling?

    <p>To select which job runs first when multiple jobs are ready.</p> Signup and view all the answers

    How does virtual memory benefit users?

    <p>It permits the execution of processes larger than the actual physical memory.</p> Signup and view all the answers

    What triggers an interrupt in modern operating systems?

    <p>The occurrence of an error or a specific user request.</p> Signup and view all the answers

    What is the role of an interrupt service routine?

    <p>To handle a specific type of interrupt when it occurs.</p> Signup and view all the answers

    During a system's operations, what does the mode bit indicate?

    <p>It differentiates between user mode and kernel mode execution.</p> Signup and view all the answers

    What happens when a user application requests a service from the operating system?

    <p>The system transitions from user mode to kernel mode.</p> Signup and view all the answers

    What is a trap in the context of operating systems?

    <p>A software-generated interrupt for error handling or requests.</p> Signup and view all the answers

    What occurs during swapping in a time-sharing system?

    <p>Processes are exchanged between main memory and disk.</p> Signup and view all the answers

    What is the primary reason users cannot control I/O devices directly?

    <p>For efficiency and protection</p> Signup and view all the answers

    Which operation is NOT typically associated with file-system manipulation?

    <p>Performing arithmetic calculations</p> Signup and view all the answers

    In what scenario would two processes communicate via message passing?

    <p>When they need to send structured data packets</p> Signup and view all the answers

    What type of error may the operating system need to handle relating to I/O devices?

    <p>Parity error on a disk</p> Signup and view all the answers

    Which function is NOT typically managed by the operating system related to resource allocation?

    <p>Regulating user permissions</p> Signup and view all the answers

    What is the role of the operating system in error detection?

    <p>To constantly detect and correct errors</p> Signup and view all the answers

    Which method allows two processes to read and write to a shared section of memory?

    <p>Shared memory</p> Signup and view all the answers

    What must the operating system do when multiple jobs are running concurrently?

    <p>Allocate resources effectively</p> Signup and view all the answers

    What occurs when a user logs onto a multitasking system like FreeBSD?

    <p>The selected shell is initiated to execute commands.</p> Signup and view all the answers

    Which system call is used by the shell to start a new process in FreeBSD?

    <p>fork()</p> Signup and view all the answers

    What is the purpose of the close() system call in file management?

    <p>To indicate that the file is no longer in use.</p> Signup and view all the answers

    In the context of device management, what happens if the required resources are not available for a process?

    <p>The process has to wait until sufficient resources are available.</p> Signup and view all the answers

    What must a process request to ensure exclusive use of a device in a multi-user system?

    <p>request()</p> Signup and view all the answers

    Which of the following best describes the command interpreter in an operating system?

    <p>It reads and executes the next command when invoked.</p> Signup and view all the answers

    What does the exec() system call do in FreeBSD?

    <p>It loads a selected program into memory and executes it.</p> Signup and view all the answers

    Which of the following is NOT a valid operation when managing files?

    <p>transfer()</p> Signup and view all the answers

    What is the primary purpose of inter process communication (IPC)?

    <p>To allow cooperating processes to exchange data and information</p> Signup and view all the answers

    In the shared-memory model, how do processes exchange information?

    <p>By reading and writing data in a common memory area</p> Signup and view all the answers

    What does the bounded buffer model imply for cooperating processes?

    <p>The consumer must wait if the buffer is empty</p> Signup and view all the answers

    What is an example of a producer in the producer-consumer problem?

    <p>The compiler, which generates assembly code</p> Signup and view all the answers

    Which feature distinguishes the message-passing model from the shared-memory model?

    <p>Communication occurs through messages rather than direct memory access</p> Signup and view all the answers

    Why might a consumer in a bounded buffer model have to wait?

    <p>Because the buffer is full</p> Signup and view all the answers

    What is a characteristic of the unbounded buffer in the producer-consumer problem?

    <p>It allows continuous production without limitations</p> Signup and view all the answers

    What is one key advantage of the message-passing approach?

    <p>It does not require any memory sharing</p> Signup and view all the answers

    Study Notes

    CPU Scheduling

    • CPU scheduling decides which task will run first when multiple jobs are ready to run simultaneously

    Time-Sharing Systems

    • Time-sharing operating systems focus on providing a reasonable response time for users
    • Swapping: Processes are moved between main memory and secondary storage (disk) to improve response time for users

    Virtual Memory

    • A technique that executes processes without them being entirely in memory
    • Allows larger programs to run than the available physical memory

    Operating System Operations

    • Modern operating systems are interrupt-driven: Wait for events to trigger actions
    • Interrupt: Hardware signal indicating an event has occurred
    • Trap: Software generated interrupt (e.g., division by zero, invalid memory access, or system service request)

    User and Kernel Modes

    • User Mode: System operating on behalf of the user
    • Kernel Mode: System operating for the OS's behalf
    • A mode bit distinguishes between user and kernel modes
    • System starts in kernel mode at boot
    • Switches to user mode to allow user programs to run
    • Switches back to kernel mode during traps or interrupts

    Privileged Instructions

    • Can only be executed in kernel mode
    • Attempts to execute privileged instructions in user mode result in a trap
    • Examples: I/O control, timer management, interrupt management

    System Calls

    • User programs use system calls to request operating system services
    • System calls are typically implemented as traps or interrupts
    • Kernel handles system calls by examining the interrupting instruction and parameters
    • System calls provide a standardized way for users to access operating system functionality.

    Timers

    • Timers interrupt the CPU after a set time interval to prevent user programs from monopolizing the CPU
    • Timer intervals can be fixed or variable

    I/O

    • Operating systems provide a way for user programs to access I/O devices
    • Users typically cannot directly control I/O devices

    File Management

    • Operating systems manage file systems, allowing programs to create, delete, read, write, and manipulate files
    • File management includes functions like open, close, read, write and rename files

    Device Management

    • Resource allocation and management is handled by the operating system
    • Processes request access to resources like main memory, disk drives, and files

    Interprocess Communication (IPC)

    • Enables cooperating processes to exchange data and information
    • Two fundamental models:
      • Shared memory: Processes share a common memory region for communication
      • Message passing: Processes exchange data packets (messages)

    Producer-Consumer Problem

    • A common paradigm where a producer process generates data that a consumer process consumes
    • Shared memory approach:
      • Producer and consumer processes share a buffer to store data
      • Buffer can be unbounded (no size limit) or bounded (fixed size)

    Message Passing

    • Processes communicate without sharing the same address space
    • Facilitates synchronous communication and synchronization

    Error Detection

    • The operating system continuously detects and corrects errors
    • Error sources: CPU hardware, memory hardware, I/O devices, and user programs
    • Corrective actions: Ensure correct and consistent computing

    Resource Allocation

    • Operating systems allocate resources such as CPU cycles, memory, files, and I/O devices to users and programs
    • Allocation methods vary based on the resource.

    Process Control

    • Operating systems manage process creation, termination, and execution.
    • Handles tasks like loading, scheduling, and synchronization

    FreeBSD Multitasking

    • Allows multiple processes to execute concurrently
    • Processes are managed through system calls like fork() and exec()
    • Shell: Accepts user commands and executes programs

    Multitasking Operating Systems

    • Allow multiple users to run programs concurrently
    • Time-sharing is a common model for multitasking, providing each user with a slice of CPU time
    • Each user is given their own virtual machine to run programs: Allows multiple users to share the same computer system while appearing to have their own private computer.

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    Description

    This quiz explores key concepts of CPU scheduling, including time-sharing systems, virtual memory, and operating system operations. Understand the differences between user mode and kernel mode, and the significance of interrupts. Test your knowledge on how modern operating systems manage multiple tasks effectively.

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