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This document contains a 6 question test on operating systems concepts. Question 1 asks about the difference between semaphores and condition variables and asks for an example where their behavior differs. Question 2 asks about calculating the maximum and minimum value of a shared variable x in a race condition scenario. Question 3 asks to write a program using semaphores to coordinate shared access to a file subject to a constraint on process numbers. Question 4 asks about the minimum number of processes that could cause a deadlock given tape drive resources. Question 5 asks about determining if a resource allocation scenario is safe or unsafe and asks about the effects of an additional request. Question 6 asks to illustrate the buddy system memory allocation and calculate

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28 views2 pages

Open Book Component

This document contains a 6 question test on operating systems concepts. Question 1 asks about the difference between semaphores and condition variables and asks for an example where their behavior differs. Question 2 asks about calculating the maximum and minimum value of a shared variable x in a race condition scenario. Question 3 asks to write a program using semaphores to coordinate shared access to a file subject to a constraint on process numbers. Question 4 asks about the minimum number of processes that could cause a deadlock given tape drive resources. Question 5 asks about determining if a resource allocation scenario is safe or unsafe and asks about the effects of an additional request. Question 6 asks to illustrate the buddy system memory allocation and calculate

Uploaded by

Vishal Mittal
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOC, PDF, TXT or read online on Scribd
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BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE, PILANI

Second Semester 2003-2004


Course Title : OPERATING SYSTEMS Course No CS C372 & IS C362
Component : Test II (Regular) Open Book Component
Weightage : 12% Max Marks: 12 Date : 09-04-2004

Note: Attempt all the Questions. Start each answer from a fresh page.

Question #1 (2 Marks)

There are a lot of similarities between semaphores and condition variables

a. What is the major difference between semaphores and condition variables?


b. Describe a situation where a semaphore P and V behaves differently than a
condition variable wait and signal.

Question #2 (2 Marks)

Consider 2 processes P0 and P1 running concurrently with race condition.


Calculate the maximum and minimum value of x.

P0 P1
for( int i=0; i<1000; i++) { for( int j=0; j<2000; j++) {
x++; x-- ;
x-- ; x++;
x++; }
}

Question #3 (3 Marks)

A file is to be shared among different processes, each of which has a unique


number. The file can be accessed simultaneously by several processes, subject to the
following constraint: The sum of all unique numbers associated with all the processes
currently accessing the file must be less than n. Write a program to coordinate the access
to the file using Semaphore.

Question #4 (1 Marks)

A computer has 16 tape drives, with n processes competing for them. Each
process may need 5 tape drives and are holding two currently. What can be the minimum
value of n that makes the system deadlock?

Operating Systems (CS C372 & IS C362) Test #2 1


Question #5 (2 Marks)

Consider the following snap shot of a system. There are no current outstanding
queued unsatisfied requests.

Available
R1 R2 R3 R4
2 1 0 0

Current Allocation Maximum Demand


Process R1 R2 R3 R4 R1 R2 R3 R4
P1 0 0 1 2 0 0 1 2
P2 2 0 0 0 2 7 5 0
P3 0 0 3 4 6 6 5 6
P4 2 3 5 4 4 3 5 6
P5 0 3 3 2 0 6 5 2

a. Is this system currently in safe or unsafe? Why?


b. If safe write down the safe sequence. If unsafe mention the processes in
unsafe state.
c. If a request from P3 arrives for (0,1,0,0), can that request be safely granted
immediately? In what state (deadlock, safe, unsafe) would immediately
granting that whole request leave the system? Which processes, if any, are or
may become deadlocked if this whole request is granted immediately?

Question #6 (2 Marks)

A 1-Mbyte block of memory is allocated using the buddy system.


a. Show the result of the following sequence in a figure. Request A (65K),
request B(210K), request C(39K), request D(120K), request E(64K), request
F(196K).
b. Show the binary tree representation after F and calculate total internal
fragmentation due to this allocation.

Operating Systems (CS C372 & IS C362) Test #2 2

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