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?

Privileged instruction. Signup and view all the answers

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

It treats the instruction as illegal and traps it. Signup and view all the answers

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

As a software interrupt. Signup and view all the answers

What is the purpose of a timer in operating systems?

To prevent user programs from monopolizing the CPU. Signup and view all the answers

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

Using a parameter associated with the interrupt. Signup and view all the answers

What is the primary purpose of CPU scheduling?

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

How does virtual memory benefit users?

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

What triggers an interrupt in modern operating systems?

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

What is the role of an interrupt service routine?

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

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

It differentiates between user mode and kernel mode execution. Signup and view all the answers

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

The system transitions from user mode to kernel mode. Signup and view all the answers

What is a trap in the context of operating systems?

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

What occurs during swapping in a time-sharing system?

Processes are exchanged between main memory and disk. Signup and view all the answers

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

For efficiency and protection Signup and view all the answers

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

Performing arithmetic calculations Signup and view all the answers

In what scenario would two processes communicate via message passing?

When they need to send structured data packets Signup and view all the answers

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

Parity error on a disk Signup and view all the answers

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

Regulating user permissions Signup and view all the answers

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

To constantly detect and correct errors Signup and view all the answers

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

Shared memory Signup and view all the answers

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

Allocate resources effectively Signup and view all the answers

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

The selected shell is initiated to execute commands. Signup and view all the answers

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

fork() Signup and view all the answers

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

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

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

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

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

request() Signup and view all the answers

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

It reads and executes the next command when invoked. Signup and view all the answers

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

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

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

transfer() Signup and view all the answers

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

To allow cooperating processes to exchange data and information Signup and view all the answers

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

By reading and writing data in a common memory area Signup and view all the answers

What does the bounded buffer model imply for cooperating processes?

The consumer must wait if the buffer is empty Signup and view all the answers

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

The compiler, which generates assembly code Signup and view all the answers

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

Communication occurs through messages rather than direct memory access Signup and view all the answers

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

Because the buffer is full Signup and view all the answers

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

It allows continuous production without limitations Signup and view all the answers

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

It does not require any memory sharing 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 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.