Hall Ticket No:
Question Paper Code: A3515
VARDHAMAN COLLEGE OF ENGINEERING
(AUTONOMOUS) B. Tech IV Semester Regular/Supplementary Examinations, May 2018
(Regulations: VCE-R15) OPERATING SYSTEMS
(Common to Computer Science and Engineering Information Technology) Date: 22 May, 2018 FN
Time: 3 hours
Max Marks: 75
Answer ONE question from each Unit
All Questions Carry Equal Marks
Unit I
1.
Discuss with examples, how the problem of maintaining coherence of cached data manifests itself in the following processing environments:
i. Single-processor systems
ii. Multiprocessor systems
iii. Distributed systems
6M
List four services provided by an operating system and explain how each of these creates convenience for users. In which cases would it be impossible for user-level programs to provide these services? Explain your answer.
9M
2.
The issue of resource utilization shows up in different forms in different types of operating systems. List what resources must be managed carefully in the following settings:
i. Work station connected to servers
ii. Mobile computers
8M
With suitable example, describe the following commands of UNIX:
i. ls
ii. mv
iii. cat
7M
Unit II
3.
Define a process. With a neat diagram, explain its states.
8M
What are the requirements for providing a solution to critical section problem? Explain.
7M
4.
Draw Gantt chart for SJF algorithm. Calculate average waiting time, average turnaround time and average response time.
Process
Arrival Time
CPU Time P1
0
3
P2
0
7
P3
2
6
P4
5
4
P5
3
5
7M
Demonstrate the following system calls with syntax:
i. msgget() ii. msgctl() iii. semop() iv. semget() 8M
Cont…2
2
Unit III
5.
The time to read or write a 32-bit memory word of 10nsec. Assume the total holes take one fourth of the 512MB memory. What is the time needed to eliminate holes by compaction?
5M
Suppose we have three processes and four resources, in the following situation:
Requested
Granted
Deficit
R1
R2
R3
R4
R1
R2
R3
R4
R1
R2
R3
R4
P1
4
2
3
1

P1
0
0
0
0

P1
4
2
3
1
P2
2
1
4
4
P2
0
1
2
2
P2
2
0
2
2
P3
5
1
2
2
P3
5
1
1
1
P3
0
0
1
1
Totals
R1
R2
R3
R4
5
2
4
4
In the above, "Totals" indicate total resources available. Using Banker's Algorithm:
i. Prove that this situation is safe by giving a schedule under which all processes can complete
ii. Under what conditions does a process in a Banker's Algorithm tableau remain runnable
iii. Suppose that we start with the above configuration and P1 asks for 3 more units of R4. Is that allocation safe? Why or why not
iv. Suppose that we start again from the above configuration and that P3 asks for 1 more unit of R3. Is that allocation safe? Why or why not
10M
6.
Bring out the significance of swapping with a suitable example.
9M
Consider the following three scenarios. One of them is best described as deadlock, one as livelock and one as starvation. Explain which is which:
i. Philosophers A and B want to pick up a chopstick. They try to be nice by waiting for one second if the other one is about to take the chopstick. They both try to pick up the chopstick, wait for a second, try again, wait again, and infinitum
ii. Process A is waiting for the result of a computation performed by process B. However, A has higher priority than and so the OS prefers A and refuses to give CPU time to B. Therefore, both A and B are stuck
iii. Processes A and B communicate through a buffer. Process A is waiting for the buffer to be full before it reads it. Process B is waiting for the buffer to be empty before it writes more data to it. Therefore, both A and B are stuck
6M
Unit IV
7.
Compare the throughput achieved by a RAID Level 5 organization with that achieved by a RAID Level 1 organization for the following:
i. Read operations on single blocks
ii. Read operations on multiple contiguous blocks
8M
Consider a file currently consisting of 100 blocks. Assume that the file index information (and index block, in the case of indexed allocation) is already in memory. Calculate how many I/O operations are required for contiguous, linked and single-level indexed strategies, if, for one block:
i. The block is removed from the beginning of the file
ii. The block is removed from the middle of the file
iii. The block is removed from the end
In the contiguous allocation case, assume there is no room to grow at the beginning, but there is room to grow at the end. Assume the contents of the new block are already in memory.
7M
Cont…3
3
8.
Explain briefly how operating system supports file locking.
7M
Suppose that a disk drive has 5,000 cylinders, numbered 0 to 4,999. The drive is currently serving a request at cylinder 2,150, and the previous request was at cylinder 1,805. The queue of pending requests, in FIFO order, is: 2,069, 1,212, 2,296, 2,800, 544, 1,618, 356, 1,523, 4,965, 3,681. Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for each of the following disk-scheduling algorithms:
i. FCFS
ii. SCAN
iii. C-LOOK
8M
Unit V
9.
Discuss the strengths and weaknesses of implementing an access matrix using access lists that are associated with objects and domains.
10M
Bring out the significance of umask with respect to file security in UNIX.
5M
10.
How are the access-matrix facility and the role-based access-control facility similar? How do they differ?
8M
What is the purpose of using a "salt" along with the user-provided password? Where should the "salt" be stored, and how should it be used?
7M