Operating Systems: Multiprogramming & Multitasking
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Questions and Answers

What is the difference between a program and a process?

A program is a passive entity stored on disk (executable file), while a process is an active entity that is being executed.

What is the degree of multiprogramming?

The degree of multiprogramming refers to the number of processes that are currently residing in memory.

Multitasking is a logical extension of multiprogramming.

True

What is the key benefit of multitasking?

<p>Multitasking provides the user with a fast response time.</p> Signup and view all the answers

What is a timeslice?

<p>A timeslice is the amount of time a process is allowed to execute before the CPU switches to another process.</p> Signup and view all the answers

Which of the following is NOT a valid process state?

<p>Idle</p> Signup and view all the answers

What is the purpose of a process control block (PCB)?

<p>A PCB serves as a data structure that represents a process in the operating system, storing important information about its state, resources, and execution context.</p> Signup and view all the answers

Which of the following is NOT a reason why a process might be terminated?

<p>System Restart</p> Signup and view all the answers

What is cascading termination?

<p>Cascading termination is a process termination model where the termination of a parent process automatically leads to the termination of all its child processes.</p> Signup and view all the answers

What is the difference between a thread and a process?

<p>Threads are lightweight processes that share the same address space with other threads within the same process, while processes are heavier and have their own independent address space.</p> Signup and view all the answers

Threads can exist outside of a process.

<p>False</p> Signup and view all the answers

What is the advantage of using threads in applications?

<p>Threads share the same process address space and resources, making inter-thread communication significantly faster than process-to-process communication.</p> Signup and view all the answers

What is the disadvantage of using threads?

<p>A problem in one thread can potentially disrupt other threads running within the same process, causing unpredictable behavior and even crashes.</p> Signup and view all the answers

Study Notes

Course Information

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

Multiprogramming

  • The operating system keeps multiple processes in memory simultaneously
  • The degree of multiprogramming is the number of processes currently in memory
  • The OS picks and begins executing a process
  • The process may wait for tasks (like I/O operations) to complete
  • In a multiprogrammed system, the OS switches easily to and executes another process.
  • Advantage: Increases CPU utilization and user satisfaction.

Multitasking/Timesharing

  • Multitasking/timesharing extends multiprogramming
  • The CPU executes multiple processes by switching between them regularly (using time slices).
  • Frequent switching leads to a fast response time for the user.

Process Concept

  • A process is a program in execution.
  • A program is a passive entity stored on disk.
  • A process is an active entity because it is loaded into memory.
  • One program can have multiple processes.
  • While text sections (code) remain the same, data, heap, and stack sections vary between processes.
  • A process can act as an environment for code (like a Java virtual machine).

Process in Memory

  • Text section: Executable code.
  • Data section: Global variables.
  • Heap: Memory allocated dynamically during runtime.
  • Stack: Temporary data (function parameters, return addresses, local variables).

Process State

  • A process changes states during its execution.
    • New: Process being created.
    • Ready: Waiting for allocation to processor.
    • Running: Instructions being executed.
    • Waiting: Waiting for an event (I/O, etc.)
    • Terminated: Process has finished execution.
  • Only one process can run on a processor core at a time.

Process Control Block (PCB)

  • Each process has a PCB, a data structure in the OS
  • Contains information like:
    • Process state (running, waiting, etc.)
    • Process number (PID)
    • Program counter (location of next instruction)
    • CPU registers
    • CPU scheduling information (priorities)
    • Scheduling queue pointers
  • The PCB is a repository for data needed to start or restart a process.

Process Scheduling

  • The CPU scheduler selects processes from the ready queue and allocates a CPU core.
  • Goal: Maximize CPU utilization and quickly switch processes.
  • Scheduling queues include:
    • Ready queue: Processes ready to run
    • Wait queue: Processes waiting for an event (I/O, etc.)
  • A new process starts in the ready queue and waits for selection for execution. (Dispatched).
  • Multiple events can cause a process to move between queues.

Context Switch

  • Switching the CPU from one process to another is a context switch.
  • Required steps: Saving state of old process and loading state of new process.
  • This involves saving and reloading the process state of the CPU.
  • A dispatcher is responsible for the context switch operations.
  • Context switch time is overhead, not actual useful work.

Operations on Processes

Process Creation

  • A process can create new processes using system calls (like fork()).
  • The created processes form a tree of processes.
  • A parent process can have multiple child processes, but each child has only one parent.
  • Options:
    • Parent and child execute concurrently.
    • Parent waits for the child to terminate.

Process Termination

  • Events causing termination:
    • Normal exit via system call (exit()).
    • Error exit (voluntary).
    • Fatal error (involuntary).
    • Killed by another process.
  • Child processes are deallocated by the operating system.

Threads

  • A thread is a lightweight process within a process.

  • Threads share the same address space.

  • This makes communication between threads very efficient, but a problem with one thread directly affects the process' viability.

  • Modern OSs allow threads to run within a process and handle more complex tasks.

  • Threads can run multiple tasks at once in a single application. – Threads run in multithreaded processes.

  • Previous processes were single-threaded.

Examples of Multithreaded Applications

  • Photo organization (thumbnail generation)
  • Web browsers (displaying images, retrieving data from network)
  • Word processors (displaying graphical content, user input response, background analysis tasks)

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Related Documents

Operating Systems 24CSCI03I Lecture Notes PDF

Description

Explore the key concepts of multiprogramming and multitasking in operating systems. Learn how the operating system manages multiple processes in memory and the advantages of efficient CPU utilization. Test your understanding of the process concept and its execution dynamics.

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