Rajiv Gandhi Proudyogiki Vishwavidyalaya(Technical University) B.E.(Sixth Semester) EXAMINATION, June, 2009(502) model question papers

Posted Date: 02 Jul 2009      Posted By:: rajesh kale    Member Level: Silver  Points: 5 (₹ 1)

# 2009 Rajiv Gandhi Proudyogiki Vishwavidyalaya(Technical University) B.E. Computer Science B.E.(Sixth Semester) EXAMINATION, June, 2009(502) Question paper

 Course: B.E. Computer Science University/board: Rajiv Gandhi Proudyogiki Vishwavidyalaya(Technical University)

CS/EI/IT-502
B.E.(Sixth Semester) EXAMINATION, June, 2009
(Common for CS,EI & IT Engg.)
OPERATING SYSTEM
Time : Three Hours
Maxmimum Marks : 100
Minimum Pas Marks : 40

Note : Attempt one question from each Unit. All questions carry equal marks. Assume suitable data
wherever necessary.

Unit - I
1.(a) What is an operating system ? Discuss the difficulties involved in writing an operating system
for a real-time environment. Give examples.
(b) Explain the differences in the degree to which the following scheduling algorithms discriminate
in favour of short processes :
(i) FCFS
(ii) Round Robin
(iii) Multilevel feedback queues
Or
2.(a) Describe three circumstances under which blocking I/O should be used. Describe three
circumstances under which non-blocking I/O should be used.
(b) Consider the following jobs:
Job Burst Time
1 10
2 29
3 3
4 7
5 12
Consider the FCFS, SJF and RR(quantum = 10) scheduling algorithms for this set of
processes. Which algorithm would give the minimum average waiting time ?

Unit - II
3.(a) What difficulties may arise when a process is rolled back as a result of Deadlock ?
(b) What are the necessary conditions for concurrence ? Give a precedence graph.

Express the graph using concurrent statement and fork/join construct.

4.(a) Explain scheduling queues with queuing diagram representation of process scheduling.
(b) Consider a system consisting of four resources of the same type that are shared by three
Processes, each of which needs at most two resources. Show that the system is deadlock free.

Unit - III
5.(a) Consider a logical address space of eight pages of 1024 words each, mapped on to a physical
memory of 32 frames :
(i) How many bits are in the logical address ?
(ii) How many bits are in the physical address ?
(b) Explain paged segmentation with its Hardware implementation ?

Or
6.(a) Assume memory partitions of 100 kB, 500 kB,200 kB, 300 kB and 600 kB(in order). How would
each of the first fit,best fit and worst fit algorithms place processes of 212 kB, 417 kB,
112 kB and 426 kB. Which algorithm makes the most efficient use of memory ?
(b) Consider a paging system with the page table stored in memory :
(i) If a memory feference takes 1.2 microseconds, how long does a paged memory reference take ?
(ii) If we add 8 associative registers and 75% of all page table reference are found in the
associative registers, what is the effective memory reference time ?
(Assume that finding a page table entry in the associative registers takes zer time, if it is
there).
Unit - IV

7.(a) Consider the following page reference strings :
1,2,3,4,5,3,4,1,6,7,8,7,8,9,7,8,9
How many page faults would occur for the following
replacement algorithms, assuming 2,4 and 5 frames being made
available?
(i) FIFO
(ii) LRU
(b) What is the need to know principle ?
Why is it important for a protection
system to adhere to this principle ?
Or
8.(a) What is the cause of thrashing ? How
does the system detect thrashing ? Once it
detects thrashing, what can the system do to
eliminate this problem ?

Unit - V
9.(a) Compare the throughput of C-SCAN and SCAN assuming a uniform distribution of requests.
(b) What problems could occur if a system allowed a file system to mounted simultaneoulsy at
more than one location ?
Or
10.(a) Consider a file system on a disk that has both logical and physical block sizes of 515 bytes.
Assume that the information about each file is already in memory. For EAch of three
(i) How is the logical to physical address mapping accomplished in this system ? ( For the
induced allocation,assume that a file is always less than 512 blocks logn).
(ii) If we are currently at logical block to ( the last block accessed was block 10) and
want to access logical block 4, how many physical blocks must be read from the disk ?

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