R09 - December, 2011 - Regular Examinations - Set - 3.

B. Tech III Year I Semester Examinations, December-2011
OPERATING SYSTEMS
(COMMON TO CSE, IT)
Time: 3 hours Max. Marks: 75
Answer any five questions
All questions carry equal marks
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1.a) State and explain different categories of system programs.
b) Explain in detail the layered approach of operating system structure. [7 8]
2.a) State and explain the various fields of a process control block.
b) Consider the following four processes, with the length of the CPU burst given in milliseconds.
Process Arrival time Burst time
P1 0 8
P2 1 4
P3 2 9
P4 3 5
Calculate the average waiting time for
i) Preemptive STF schedule
ii) Non preemptive STF schedule. [7 8]
3.a) What is a semaphore?
b) Explain the bounded buffer problem and how semaphores can be used an a solution to this problem. [7 8]
4.a) What is paging? Explain the basic method for implementing paging.
b) Consider the following reference string:
7,0,1,2,0,3,0,4,2,3,0,3,2,1,2,0,1,7,0,1assume there are three frames which are initially empty. Using FIFO page replacement algorithm determine the number of page fonts for the reference string above. Provide necessary diagram for page frames. [7 8]
5. Write short notes on the following:
a) Mutual exclusion
b) Hold and wait
c) No preemption
d) Circular wait. [15]
6. Explain the three allocation methods in file system implementation Illustrate with proper diagram. [15]

7.a) Consider a disk queue with requests for I/O to blocks on cylinders 98, 183, 37,122,14,124,65,67 in that order. Assume the disk head is initially at cylinder 53.
i) Show diagrammatically as well as explain the FCFS disk scheduling and SSTF disk scheduling
ii) Find out the total head movement for FCFS and SSTF algorithm
iii) Describe performance of both the algorithms.
b) Write short notes on STREAMS. [15]
8.a) Describe the goals of system protection.
b) Explain in detail about program threats. [7 8]
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