Basic CS-Operating System [3i Infotech Placement]: Sample Questions 11 - 11 of 89

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Question 11

Operating System

Describe in Detail


What is Thread? Define Kernel vs User.


  • Thread is smallest unit of processing performed in an OS.
  • Flow of execution through the process code.
  • Has its own context- program counter, system registers, and stack.
  • Also called a light weight process.
  • Provides improved application performance through parallelism.
  • Exists within a process - that is, a single process may contain multiple threads.
  • Multiple threads running concurrently- multithreading is similar to multitasking.

Advantages of thread:

  • Minimize context switching time.
  • Concurrency within a process.
  • Efficient communication.
  • Economy
  • Utilization of multiprocessor architectures to a greater efficiency.
  • There are two kinds of threads:
Difference between Kernel Mode and User Mode
Kernel ModeUser Mode
Executing code has complete and unrestricted access to the underlying hardware.Executing code has no ability to directly access hardware or reference memory.
Generally reserved for the lowest-level, most trusted functions of the operating system.Code running in user mode must delegate to system API to access hardware or memory.

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