Operating Systems Basics Quiz

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Questions and Answers

What is meant by the degree of multiprogramming?

  • The number of tasks queued for execution.
  • The number of processes currently executing on the CPU.
  • The number of processes in memory simultaneously. (correct)
  • The number of CPU cores available.

Which of the following statements correctly describes multitasking?

  • It is only applicable to single-core processors.
  • It allows multiple programs to run completely at the same time.
  • It executes multiple processes by switching among them after a timeslice. (correct)
  • It creates a cloned instance of each program in memory.

What is the primary advantage of multiprogramming?

  • To allow a single process to monopolize CPU time.
  • To increase overall CPU utilization. (correct)
  • To decrease user interaction with processes.
  • To minimize the number of processes in memory.

How does a process differ from a program?

<p>A process is a program in execution, whereas a program is a passive entity. (B)</p> Signup and view all the answers

What is the purpose of the Process Control Block (PCB)?

<p>To store data needed to start or restart a process. (A)</p> Signup and view all the answers

Which of the following states indicates that a process has finished execution?

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

What indicates that the stack and heap sections of memory can change size during execution?

<p>They can grow and shrink dynamically without overlapping. (D)</p> Signup and view all the answers

Which is true about the CPU scheduling goal?

<p>To maximize CPU usage and quickly dispatch processes. (A)</p> Signup and view all the answers

Which section of process memory is primarily used for global variables?

<p>Data section (D)</p> Signup and view all the answers

In which state does a process wait for an event to occur, such as I/O completion?

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

What is true about how many processes can run on a processor core at any given time?

<p>Only one process can be executing on a core at a time. (B)</p> Signup and view all the answers

What does the CPU scheduler primarily select from?

<p>Processes in the ready queue. (B)</p> Signup and view all the answers

What advantage do threads offer in a multicore system?

<p>They can execute several CPU-intensive tasks in parallel. (D)</p> Signup and view all the answers

Which statement accurately reflects a characteristic of threads?

<p>Each thread has its own Program Counter and stack. (B)</p> Signup and view all the answers

What is a primary disadvantage of threads sharing the same address space?

<p>It can cause issues with thread synchronization. (D)</p> Signup and view all the answers

In which scenario would a thread likely be utilized?

<p>When an application needs to perform multiple tasks simultaneously. (C)</p> Signup and view all the answers

What does it mean that threads are lightweight processes?

<p>They have their own ID but share resources with other threads. (A)</p> Signup and view all the answers

What is the main responsibility of a dispatcher in process scheduling?

<p>Switching the CPU core to another process (C)</p> Signup and view all the answers

Which of the following statements about context switch time is true?

<p>Context switch time represents pure overhead with no useful work performed. (C)</p> Signup and view all the answers

In a tree of processes, which of these statements is correct?

<p>Parent and children processes execute concurrently by default. (D)</p> Signup and view all the answers

Which of the following best describes process termination?

<p>It results in the removal of the process from all queues. (B)</p> Signup and view all the answers

What must occur when a CPU switches to a new process?

<p>The state of the old process must be saved. (D)</p> Signup and view all the answers

Which of the following is NOT a resource typically required by a child process?

<p>Execution of parent processes (C)</p> Signup and view all the answers

What is a key factor that influences the length of context switch time?

<p>Memory speed and number of registers to copy. (D)</p> Signup and view all the answers

Which process always has a PID of 1 in a Linux system?

<p>The systemd process (D)</p> Signup and view all the answers

What is the consequence of a parent process terminating if certain operating systems do not allow child processes to exist independently?

<p>No child processes can continue, leading to cascading termination. (B)</p> Signup and view all the answers

Which system call is used for a process to request its deletion when it completes its work normally?

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

What scenario could lead to a process experiencing a fatal error?

<p>The process attempts to access nonexistent memory. (C)</p> Signup and view all the answers

Which of the following best describes the nature of multithreaded applications?

<p>Applications can execute more than one task simultaneously using multiple threads. (A)</p> Signup and view all the answers

What is the role of resource allocation in parent-child process relationships?

<p>The parent may partition its resources or allow shared resources among children. (B)</p> Signup and view all the answers

In which situation would a process execute an error exit voluntarily?

<p>The user provides a command that references a nonexistent file. (D)</p> Signup and view all the answers

What is a potential reason for a parent process to terminate one of its child processes?

<p>The task assigned to the child is no longer needed. (D)</p> Signup and view all the answers

Which function in Win32 is equivalent to the UNIX kill system call for terminating a process?

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

Flashcards

Multiprogramming

Technique where the operating system simultaneously manages several processes (programs) in memory, allowing them to share CPU time. It increases CPU utilization and user satisfaction.

Multitasking/Timesharing

A logical extension of multiprogramming where the CPU rapidly switches between multiple processes, giving each a small time slice. This creates the illusion of multiple programs running at the same time, providing fast response times for users.

Process

A program in execution. An executable file is a passive entity that is loaded into memory to become an active process.

One program with multiple processes

A program that consists of multiple processes. Each process has its own memory space for data and instructions.

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Degree of Multiprogramming

The number of processes in memory at a given time. This directly affects the overall performance and resource utilization of the system.

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Text Section

The section of memory that stores the executable code of a program. It's essentially the instructions for the program to run.

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Data Section

A section of memory that stores global variables, which are accessible from anywhere within the program.

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Stack

A section of memory that stores temporary data used during function calls. This includes function parameters, return addresses, and local variables.

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Heap

A section of memory dynamically allocated during program runtime. Programmers can request memory from the heap as needed to store data. Think of this as a flexible, dynamic storage area.

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Fixed Size Memory Sections

The size of this section remains constant during a program's execution.

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Dynamic Memory Sections

The stack and heap sections can grow and shrink during program execution, but they never overlap.

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New State

The process is being created by the operating system.

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Ready State

The process is ready to be executed but waiting for the CPU to be assigned to it.

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Context Switch

The action of switching the CPU from one process to another.

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Process Control Block (PCB)

The data structure that holds information about a process, including its ID, memory address, and current state.

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Context Switch Time

The time required to save the old process's state and load the new process's state during a context switch.

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Dispatcher

A system component responsible for executing context switches. It handles the saving and loading of process states.

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Process Migration

The event that triggers a process to be moved from one queue to another.

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Process Creation

The creation of a new process by an existing process, forming a hierarchical relationship between them.

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Parent Process

A process that creates other processes, forming a tree-like structure where each child has only one parent.

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Child Process

A process created by a parent process, forming a tree-like structure where each has only one parent.

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Resource Restriction in Child Processes

A child process is limited to a specific set of resources provided by its parent process, preventing resource overload and ensuring system stability.

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Normal/Error Exit (Voluntary Termination)

A process voluntarily terminates its execution when its task is completed or upon encountering an error.

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Fatal Error (Involuntary Termination)

Process termination due to unexpected events like illegal instructions or incorrect memory access, leading to involuntary shutdown.

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Process Termination by Another Process (Involuntary)

One process can terminate another process using specific system calls, like 'kill' in UNIX or 'TerminateProcess()' in Windows.

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Parent Terminating a Child Process

A parent process can terminate a child process for reasons such as resource overuse or task completion.

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Cascading Termination

If a parent process ends, its associated child processes are also automatically terminated, ensuring proper resource cleanup.

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Threads in Processes

Operating systems allow processes to execute multiple threads of control, allowing for the execution of several tasks concurrently within a single process.

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Multithreading for Concurrent Tasks

A process can perform multiple tasks concurrently by running multiple threads, each handling a specific task within the process.

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What is a thread?

A lightweight process that shares code, data, and OS resources but has its own ID, PC, register set, and stack.

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What's the relationship between a thread and a process?

Each thread belongs to a specific process and can't exist independently. Threads from different processes cannot interact directly.

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What are the benefits and drawbacks of threads sharing memory?

Because threads within a process share the same memory space, communication between them is very efficient. However, a problem with one thread can affect the entire process.

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How do threads help with multi-core systems?

Applications can use threads to take advantage of multiple processor cores, speeding up execution by running different tasks concurrently.

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Give an example of how threads are used in a word processor.

A word processor might use one thread for displaying graphics, another for handling user input, and a third for spell-checking, all running simultaneously.

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Study Notes

Operating Systems Course Information

  • Course title: Operating Systems
  • Course code: 24CSC1031
  • Instructor: Wessam El-Behaidy
  • Main text reference: Operating System Concepts, Abraham Silberschatz, 10th Edition

Multiprogramming

  • Idea: The operating system keeps multiple processes in memory at once.
  • Degree of multiprogramming: The number of processes currently in memory.
  • System behavior: The OS switches between processes to improve CPU utilization and user satisfaction.
  • Key advantage: Increased CPU utilization.
  • Further advantage: Improved user satisfaction.

Multitasking/Timesharing

  • Description: A logical extension of multiprogramming.
  • CPU behavior: The CPU switches between multiple processes frequently using time slices.
  • Result: Provides users with a faster response time.

Process Concept

  • Definition: A program in execution.
  • Program state: Passive entity stored on a disk (executable file).
  • Process state: Active entity loaded to memory.
  • Program-Process conversion: Occurs when the executable file is loaded to memory.

Process Structure

  • Multiple processes per program: The same program may have several processes running.
  • Separate Resources: Processes have separate data sections.
  • Process environment: A process can be an environment for other code like a JVM

Process in Memory

  • Text section: Executable code.
  • Data section: Global variables.
  • Stack: Temporary data (function parameters, return addresses, local variables).
  • Heap: Memory dynamically allocated during runtime.
  • Fixed size: Text and data sections have fixed sizes.
  • Dynamic size: Stack and heap dynamically change size during runtime; they never overlap.

Process States

  • New: Process being created.
  • Ready: Waiting to be assigned to a processor.
  • Running: Instructions being executed.
  • Waiting: Waiting for an event to occur.
  • Terminated: Process has finished execution.
  • Important information: Only one process can run on a processor core at once. Multiple processes can exist in ready and waiting states.

Process Control Block (PCB)

  • Description: Data structure representing a process in the operating system.
  • Components: Process state, process number (PID), program counter, CPU registers, memory limits, scheduling information, scheduling queue pointers, list of open files.
  • Purpose: Serves as a repository for the data needed to start or restart a process.

Process Scheduling

  • Function: The CPU scheduler selects processes from the ready queue and allocates a CPU core to one of them.
  • Goals: Maximize CPU utilization and quickly switch between processes.
  • Queues:
  • Ready queue: Processes in memory, ready for execution.
  • Wait queue: Processes waiting for an event (e.g., input/output).

Context Switching

  • Description: Switching the CPU from one process to another.
  • Saving and loading process state: The old process's state needs to be saved and new process state loaded.
  • Dispatcher: The dispatcher is responsible for context-switching.
  • Overhead: Time spent doing context switching is overhead meaning it does not perform the tasks

Operations on Processes

  • Process creation: One process creates other processes.
  • Process termination: When a process finishes or needs to be killed.

Process Creation

  • Method: A process creates other processes, forming a process tree.
  • Parent and child process: A parent may have multiple children, but a child only one parent.
  • Concurrent execution: Parent and child processes often execute concurrently.
  • Waiting for child: Parent process may wait till the child completes.

Process Termination

  • Common reasons: Normal exit, error exit, fatal error, kill by an another process.
  • Cascating termination: When a process terminates, child processes also terminates.

Threads

  • Lightweight Processes: Threads share the same address space with other threads in the same process.
  • Sharing: Threads share code, data, heap sections, OS resources.
  • Multiple threads per process: A process can have multiple threads, enabling multiple tasks at once.

Examples of Multithreaded Applications

  • Photo thumbnails: Creating thumbnails for large collections of images (each image in a different thread, thus faster).
  • Web browser (One thread for browsing, another for retrieving data).
  • Word processor (One thread for displaying text, another for processing).

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