Anna University - November December 2018 CS6401 Operating Systems Fourth Semester Regulation 2013 - End Semester Examination Questions with Answers
|
Exam |
B.E/B.Tech. (Full Time) DEGREE EXAMINATION |
|
Academic Year |
November December 2018 |
|
Subject Code |
CS6401 |
|
Subject Name |
Operating Systems |
|
Branch |
Computer Science and Engineering |
|
Semester |
Fourth Semester |
|
Regulation |
2013 |
B.E / B.Tech. (Full Time) DEGREE END SEMESTER EXAMINATIONS, Nov / Dec 2018
Computer Science and Engineering
Fourth Semester
CS6401 – Operating Systems
(Regulation 2013)
Time : 3 Hours Answer A L L Questions Max. Marks 100
PART-A (10 x 2 = 20 Marks)
1. Some computer systems do not provide a privileged mode of operation in hardware. Is it possible to construct a secure operating system for these computer systems?
2. Can traps be generated intentionally by a user program? If so, for what purpose?
Answer:
A trap is a software-generated interrupt. A trap
can be generated intentionally by a user program. It can be used to call
operating system routines or to catch arithmetic errors.
3. What is the meaning of the term busy waiting?
Answer:
Busy-waiting, busy-looping or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available.
When a task cannot continue until an event
occurs, and so repeatedly polls to see if the event has occurred, it is said to
be busy waiting. The key idea is that the task continues to consume processor
time by repeatedly checking the condition. Examples of busy waiting include
software synchronization algorithms, such as the bakery algorithm, and spin
locks using hardware synchronization primitives such as test_and_set.
4. Can a multithreaded solution using multiple user-level threads achieve better performance on a multiprocessor system than on a single-processor system?
Answer:
No. A multithreaded system comprising of
multiple user level threads cannot make use of the different processors in a multiprocessor
system simultaneously. Because, user level threads are interpreted by the OS as
only a single process and will not schedule different threads of the process on
separate processors. That strongly suggests that there is no performance
benefit to be had in this situation.
5. Under what circumstances would a user be better off using a timesharing system rather than a PC or single-user workstation?
Answer:
When there are few other users, the task is large, and the hardware is fast, time-sharing makes sense. The full power of the system can be brought to bear on the user’s problem. The problem can be solved faster than on a personal computer. Another case occurs when lots of other users need resources at the same time.
A personal computer is best when the job is small enough to be executed reasonably on it and when performance is sufficient to execute the program to the user’s satisfaction.
6. State the effect of Thrashing in an operating system.
Answer:
A process that is spending more time paging than executing is said to be thrashing.
Thrashing leads to low CPU utilization. It causes slowdown of the system performance in terms of data transfer between the primary and secondary.
7. Mention the significance of LDT and GDT in segmentation.
8. List the major attributes and operations of a file system.
9. Do FAT file system advantageous? Justify your answer.
10. Mention the importance of a Kernel in LINUX Operating system.
PART B — (5 x 13 = 65 marks)
11. (a) (i) Explain the various types of system calls with an example for each. (8)
(ii) Discuss the functionality of system boot with respect to an Operating System. : (5)
OR
(b) Discuss the essential properties of the following types of systems
(i) Time sharing systems. (4)
(ii) Multi-processor systems. (4)
(iii) Distributed Systems. ~ (5)
12. (a) (i) Explain why interrupts are not appropriate for implementing synchronization primitives in multiprocessor systems. (7)
(ii) Compute the average waiting time for the processes using non-preemptive SJF scheduling algorithm. (5)
|
Process |
Arrival time |
Burst time |
|
P1 |
0.0 |
7 |
|
P2 |
2.0 |
4 |
|
P3 |
4.0 |
1 |
|
P4 |
5.0 |
4 |
OR
(b) Discuss how the following pairs of scheduling criteria conflict in certain settings.
(i) CPU utilization and response time. (4)
(ii) Average turnaround time and maximum waiting time. (5)
(iii) I/O device utilization and CPU utilization. (4)
13. (a) Compare paging with segmentation in terms of the amount of memory required by the address translation structures in order to convert virtual addresses to physical addresses.
OR
(b) Most systems allow programs to allocate more memory to its address space during execution. Data allocated in the heap segments of programs is an example of such allocated memory. What is required to support dynamic memory allocation in the following schemes?
(i) Contiguous memory allocation (4)
(ii) Pure segmentation (5)
(iii) Pure paging. (4)
14. (a) Consider a file system where a file can be deleted and its disk space reclaimed while links to that file still exist. What problems may occur if a new file is created in the same storage area or with the same absolute path name? How can these problems be avoided?
OR
(b) Illustrate an application that could benefit from operating system support for random access to indexed files.
15. (a) UNIX coordinates the activities of the kernel I/O components by manipulating shared in-kernel data structures, whereas Windows NT uses object-oriented message passing between kernel 1/0 components. Discuss three pros and three cons of each approach.
OR
(b) Discuss virtualization techniques used in different operating systems.
PART C — (1 x 15 = 15 marks)
16. (a) Which of the following scheduling algorithms could result in starvation?
(i) First-come, first-served (5)
(ii) Shortest job first (5)
(iii) Round robin (5)
Detail with Justification.
OR
(b) Outline a solution using semaphores to solve dinning philosopher problem. (15)
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