Basic CS-Operating System [TCS Placement]: Sample Questions 3 - 4 of 35

Get unlimited access to the best preparation resource for competitive exams : get questions, notes, tests, video lectures and more- for all subjects of your exam.

Question 3

Operating System

Describe in Detail


What is a trap and trapdoor?



  • The execution of an instruction that intended for user programs and transfers control to the operating system.
  • Trap causes branch to OS code and a switch to kernel mode.
  • When in kernel mode, a trap handler is executed to service the request.
  • Restarted at the address following the address causing the trap.
  • Example: any System call.
Given the Image is Define the Traps Example


  • Secret undocumented entry point to the program.
  • An example of such feature is so called back door.
  • This enables intrusion to the target by passing user authentication methods.
  • A hole in the security of a system deliberately left in place by designers or maintainers.
  • Trapdoor allows unauthorized access to the system.
  • Only purpose of a trap door is to “bypass” internal controls.
  • It is up to the attacker to determine how this circumvention of control can be utilized for his benefit.
Given the Image is Define the Trap Doors

Question 4

Operating System

Write in Short

Short Answer▾

What are the reasons for process Creation?


Process creation happens due to:

  1. New batch job
    • The operating system is provided with a batch job control stream, usually on tape or disk.
    • When the operating system is prepared to take on new work, it will read the next sequence of job control commands.
  2. Interactive logon

    A user at a terminal logs on to the system.

  3. Created by OS to provide a service

    The Operating system can create a process to perform a function on behalf of a user program, without the user having to wait.

  4. Spawned by existing process

    For purposes of modularity or to exploit parallelism, a user program can dictate the creation of a number of processes.

Developed by: