Operating System


Time : 3 hours                                                                         Max. marks : 100


Answer ALL Questions


                                                                     PART-A                         10×2 = 20 marks 

1. Mention any two essential properties of real time systems.

2. Processes call the operating system with system call interrupt instructions. Why      can’t processes make ordinary procedure calls to the operating systems?

3. What is meant by the context of a process?

4. Mention the methods for deadlock recovery in a system.

5. Consider the following set of processes, with the length of the CPU-burst time and      the arrival time given in milliseconds:

Process                        Arrival Time                            Burst Time

______                       ___________                          __________


  P1                                     0                                           75

  P2                                    10                                          40

  P3                                    10                                          25

  P4                                     80                                          20

  P5                                     85                                          45

  a. Draw a Gantt chart illustrating the execution of these processes using preemptive SJF scheduling algorithm.

6. What is the relationship between program locality and TLB hit rate?

7. What is Belady’s anomaly?

8. What is thrashing?

9. Mention the advantages and disadvantages of continuous allocation of files.

10. List the main components of a Linux system.


PART-B                                   5×16 = 80 marks


11.(i) Explain the MS-DOS system structure with a neat diagram.                    (8)

(ii) Write notes on Hardware protection.                                                        (8)


12.(a) (i)Describe the actions taken by a kernel to context switch between kernel-level threads.                                                                                                         (4)

      (ii) Consider the following snapshot of a system:

      Allocation                                     Max                                         Available

    __________                        ____                                        ________

       A B C D                        A B C D                                     A B C D


P0   0  0  1  2                        0  0  1  2                                      1  5  2  0

P1   1  0  0  0                        1  7  5  0                                      

P2   1  3  5  4                        2  3  5  6

P3   0  6  3  2                        0  6  5  2

P4   0  0  1  4                        0  6  5  6


Answer the following questions using the banker’s algorithm.


a. What is the content of matrix Need?                                                        (2)

b. Is the system in a safe state? If yes, give the safe sequence.                    (2)

c. If a request from process P1 arrives for (0,4,2,0) can the request be granted immediately?                                                                                      (4)


(iii)Distinguish between short term, long term and medium term scheduling.(4)



b) (i) How does a semaphore solve the critical section problem? Discuss whether semaphores satisfy the three requirements for a solution to the critical section problem.                                                                                                                (8)

    (ii) A barbershop consists of a waiting room with n chairs and the barber room containing the barber chair. If there are no customers to be served, the barber goes to sleep. If a customer enters the barbershop and all chairs are occupied, then the customer leaves the shop. If the barber is busy but chairs are available, then the customer sits in one of the free chairs. If the barber is asleep, the customer wakes up the barber. Write a program to coordinate the barber and the customers. (8)


13.a. (i) Given memory partitions of 100K, 500 K, 200 K, and 600K (in order), how would each of the First-fit, Best-fit, and Worst-fit algorithms place processes of 212K, 417K, 112K, and 426K (in order)? Which algorithm makes the most efficient use of memory?                                                                          (8)

    (ii) Write down the different issues in real time scheduling.                      (8)




b. (i)Explain segmentation with a neat diagram.                                            (8)

    (ii) Consider a variation of round-robin we will call progressive round-robin. In progressive round-robin, each process has its own time quantum. This starts out at 50 ms, and increases by 50 ms each time it goes through the round-robin queue. Give the advantages and disadvantages of this variant over ordinary round-robin.                                                                                                                           (8)


14. a.  What is the cause of thrashing? Explain the methods by which thrashing could be controlled.                                                                                                   (16)


b. Describe different schemes for defining the logical structure of a directory.                                                                                                                        (16)


15.a. Discuss on the following disk scheduling algorithms:

 Shortest Seek Time First, First Come First Served, SCAN, C- LOOK. (16)



b. Explain briefly how process management is done in Linux.                      (16)

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