Friday, 24 April 2020

Operating systems multiple choice questions for exams - Set 11

Operating systems exams - multiple choice questions (MCQ) and answers



Operating Systems MCQ Questions and Answers – Set 11

1. The primary difference between user-level threads and kernel threads is ______
(a) User level threads do not use OS services via system calls, whereas kernel threads require system calls.
(b) User level threads are independent of each other, whereas kernel threads can write into each other’s memory space.
(c) User level threads require memory management where kernel threads do not.
(d) None of above.

View Answer

Answer: (a)                    
User level threads do not use OS services via system calls, whereas kernel threads require system calls. Kernel-level threads require a system call for the switch to occur; user-level threads do not.
Other differences are;
  • User level threads are faster to create whereas kernel level threads are slower to create.
  • User level threads are able to run on any OS, and kernel level threads are specific to OS.
  • Less context switch time for user level threads and more for kernel level threads.

2. CPU burst distribution is generally characterized as
(a) Constant
(b) Linear
(c) Polynomial
(d) Exponential or hyper-exponential

View Answer

Answer: (d) Exponential or hyper-exponential

CPU burst distribution is mostly exponential. The length of CPU bursts measured across all processes is distributed approximately exponentially, with short bursts much more likely than long bursts.

This pattern is somewhat true even for single processes (think of a program that has to do several I/O operations in a row after a long computation), but the distribution may be shifted depending on whether the process is CPU bound (mostly wanting to use the CPU for long computations) or I/O bound (mostly waiting for I/O).

3. Which of the following is not a CPU scheduling criterion?
(a) CPU utilization
(b) Burst time
(c) Throughput
(d) Response time

View Answer

Answer: (b) Burst time      
Burst time is the amount of time required by a process for executing on CPU.

CPU scheduling criterions

CPU utilization (use of CPU), Throughput (number of processes completed per unit time), and Response time (time taken in an interactive program from the issuance of a command to the commencement of a response to that command) are the CPU scheduling criterions.
Other such criterions are Turnaround time and waiting time.

4. Which among the following is a preemptive only scheduling algorithm?
(a) RR
(b) FCFS
(c) SJF
(d) None of the above

View Answer

Answer: (a) Round Robin (RR)   
Round robin algorithm is the preemptive scheduling algorithm.
FCFS is preemptive and SJF is both preemptive and non-preemptive scheduling algorithm.

5. If the time quantum is very large, a RR (Round-Robin) scheduling is the same as:
(a) FCFS
(b) SJF
(c) SRTF
(d) Multi-level queue

View Answer

Answer: (a) FCFS         
The performance of round robin scheduling algorithm depends on the time quantum selected. If the time quantum is very large, then RR is same as FCFS. Because with large time quantum it is likely to finish each process as they arrive. Such way it is showing the behavior of FCFS algorithm.


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