Operating Systems CT-1 Sep_2024

A thread is usually defined as a ‘light weight process’ because an operating system (OS) maintains smaller data structures for a thread than for a process. In relation to this, which of the followings is TRUE?

• 1. On per thread basis, the OS maintains only scheduling and accounting information

• 1. On per-thread basis, the OS does not maintain virtual memory state

• 1. On per-thread basis, the OS maintains only CPU register state

• 1. The OS does not maintain a separate stack for each thread

15. System calls are invoked by using

• 15. software interrupt

• 15. polling

• 15. indirect jump

• 15. a privileged instruction

Which of the following statements are true?
I. Shortest remaining time first scheduling may cause starvation
II. Preemptive scheduling may cause starvation
III. Round robin is better than FCFS in terms of response time

• I only
  

• I and III only

• II and III only

• I, II and III

An operating system uses Shortest Remaining Time first (SRT) process scheduling algorithm. Consider the arrival times and execution times for the following processes:

Consider the following statements with respect to user-level threads and kernel supported threads
i. context switch is faster with kernel-supported threads
ii. for user-level threads, a system call can block the entire process
iii. Kernel supported threads can be scheduled independently
iv. User level threads are transparent to the kernel

Which of the above statements are true?

• (ii), (iii) and (iv) only

• (ii) and (iii) only

• (i) and (iii) only

• (i) and (ii) only

Which of the following need not necessarily be saved on a context switch between processes?

• General purpose registers

• Program counter

• Translation look-aside buffer

• All of the above

Consider the following statements about user level threads and kernel level threads. Which one of the following statement is FALSE?

• Context switch time is longer for kernel level threads than for user level threads

• User level threads do not need any hardware support

• Related kernel level threads can be scheduled on different processors in a multi-processor system

• Blocking one kernel level thread blocks all related threads

Consider three CPU-intensive processes, which require 10, 20 and 30 time units and arrive at times 0, 2 and 6, respectively. How many context switches are needed if the operating system implements a shortest remaining time first scheduling algorithm? Do not count the context switches at time zero and at the end.

• 1

• 2

• 3

• 4

Who provides the interface to access the services of the operating system?

• 1. API

• 1. System call

• Library

• 1. Assembly instruction

The maximum number of processes that can be in Ready state for a computer system with n CPUs is

• n

• n^2

• 2^n

• Independent of n