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B.E. / B.Tech DEGREE EXAMINATION, APRIL/MAY 2008

Fifth Semester

Information Technology

CS1252 - OPERATING SYSTEMS

(Regulation 2004)

Time: Three hours Maximum: 100 marks

Answer ALL questions.

PART A – (10 x 2=20 marks)

1.Define Real Time Operating System.

2.Define SYSTEM CALLS.

3.What do you mean by a critical section problem?

4.Define the use of monitor.

5.Describe the four necessary conditions for deadlocks.

6.Why should paging be used by operating systems?

7.Define virtual memory.

8.What is the cause of thrashing?

9.What is the Kernel of an operating system?

10.Mention the importance of swap-space management.

PART B - (5 x 16 = 80 marks)

11. (a) (i)How does multi programming help in achieving improved utilization of a

computer

system?[Marks 8]

(ii)With necessary diagram explain the term "process" from the operating system

Or

(b) (i)Briefly explain the four major functions of an operating system.[Marks 8]

(ii)Give the main feature of the following types of OS outlining their limitations and

strengths : Interactive Time sharing OS, Real Time OS. [ marks 8]

12. (a) Consider the following set of processes, with the length of CPU-burst time

given in millisecond. [marks 16]

Process Burst time Priority

p1 10 3

p2 1 1

p3 2 3

p4 1 4

p5 5 2

The processes are assumed to have arrived in order p1,p2,p3,p4,p5 all at time 0. (i)

Draw Gantt chats illustrating the execution of these processes using FCFS, SJF, a

non-preemptive priority ( a smaller priority number implies a higher priority) and RR

(quantum=1) scheduling (ii) What is the turn around time of each process for each of

the scheduling algorithms in part (i)?

Or

(b) (i)What two advantages do threads have over multiple processes?

What major disadvantage do they have? Suggest one application that would benefit

from the use of threads, and one that would not. [marks 6]

(ii) Define the requirement of the correct solution.How semaphor es are used to solve

dining philosophers problem. [marks 10]

13. (a) An operating system contains three resource classes, namely R1, R2 and R3.

The number of resource units in these classes is 7,7 and 10 respectively.The current

resource allocation state is as shown below :[marks 16]

Process Allocated Resources Maximum Requirement

R1 R2 R3 R1 R2 R3

P2 2 0 3 4 3 3

P3 1 2 4 3 4 4

(i) Is the current allocation state safe?[Marks 4]

(ii)Would the following requests be granted in the current state?

(1) Process P1 requests(1, 1, 0) [Marks 4]

(2) Process P3 requests(0, 1, 0) [Marks 4]

(3) Process P2 requests(0, 1, 0) [Marks 4]

Or

(b) (i)Explain some of the most common techniques for structuring the page table.

[marks 8]

(ii)Explain the princples of segmentation with examples. [marks 8]

14. (a) Consider the following page reference string : [marks 16]

1,2,7,8,3,4,2,1,4,2,5,6. How many page faukts would occur for the following page

replacement algorithms, assuming an allocation of 3 frames?

(i) LRU [marks 5]

(ii) FIFO [marks 5]

(iii) Optimal. [marks 6]

Or

(b) (i) Explain the concept of demand paging. [marks 8]

(ii) How does the system detect trashing? Once it detect trashing what the system do

to eliminate this problem? [marks 8]

15. (a) (i) Describe the salient features of the file system of UNIX. [marks 8]

(ii)Explain UNIX buffer cache mechanism. [marks 8]