Rajiv Gandhi Proudyogiki Vishwavidyalaya 2009-6th Sem B.E Computer Science .(ester) , e, (502) - exam paper

CS/EI/IT-502
B.E.(Sixth Semester) EXAMINATION, June, 2009
(Common for CS,EI & IT Engg.)
OPERATING SYSTEM
Time : 3 Hours
Maxmimum Marks : 100
Minimum Pas Marks : 40

Note : Attempt 1 ques. from every Unit. All ques. carry equal marks. presume suitable data
wherever necessary.

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

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


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

4.(a) discuss scheduling queues with queuing diagram representation of process scheduling.
(b) Consider a system consisting of 4 resources of the identical kind that are shared by 3
Processes, every of which needs at most 2 resources. Show that the system is deadlock free.

Unit - III
5.(a) Consider a logical address space of 8 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) discuss paged segmentation with its Hardware implementation ?

Or
6.(a) presume memory partitions of 100 kB, 500 kB,200 kB, 300 kB and 600 kB(in order). How would
every of the 1st 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 eight associative registers and 75% of all page table reference are obtained 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 subsequent 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 subsequent
replacement algorithms, assuming 2,4 and five 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 reason of thrashing ? How
does the system detect thrashing ? Once it
detects thrashing, what can the system do to
eliminate this issue ?

Unit - V
9.(a) Compare the throughput of C-SCAN and SCAN assuming a uniform distribution of requests.
(b) What issues could occur if a system allowed a file system to mounted simultaneoulsy at
more than 1 location ?
Or
10.(a) Consider a file system on a disk that has both logical and physical block sizes of 515 bytes.
presume that the info about every file is already in memory. For every of 3
allocation strategies(contiguous,linked and indexed) ans these ques. :
(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 learn from the disk ?

Earning:   Approval pending.