MODEL PAPER
SECOND SEMESTER, M. Sc INFORMATION TECHNOLOGY

Paper - IV (MIT - 204): Operating System

1. Question.


1. In a multiprogramming and time sharing environment, several users share the system simultaneously. This situation can result in various security problems.
   1. What are two such problems
   2. Can we ensure the same degree of security in a time-shared machine as we have in a dedicated machine? Explain your answer.
2. Using system calls, write a program either in C or C⁺⁺ that reads data from one file and copies it to another file
2. Question.


1. The producer-consmer algorithm in the book allows only n-1 buffers to be full at any one time. Modify the algorithm to allow all buffers to be utilized fully.
2. Provide two programming examples of multithreading that do not improve performance over a single threaded solution.
3. Question.


1. Write a monitor solution to the dinning-philosopher problem.
2. Consider the following snapshot of a system: -
   
   

   Allocation A B C D P0 0 0 1 2 P1 1 0 0 0 P2 1 3 5 4 P3 0 6 3 2 P4 0 0 1 4

   Max A B C D 0 0 1 2 1 7 5 0 2 3 5 6 0 6 5 2 0 6 5 6

   Available A B C D 1 5 2 0

   
   Answer the following questions using Banker's algorithm:
   
   1. What is the content of the matrix need?
   2. Is the system in a safe state?
   3. If a request from P1 arrives for (0, 4, 2, 0), can the request be granted immediately?
4. Question.


1. Consider a system where a program can be separated into two parts: Code and data. The CPU knows whether it wants an instruction (instruction fetch) or data (data fetch or store). Therefore, two base-limit register pairs are provided: one for instruction and one for data. The instruction base-limit register pair is automatically set to read only, so programs can be shared among different users. Discuss the advantages and disadvantages of this scheme.
2. Consider the following page-reference string:
   1, 2, 3, 4, 2, 1, 5, 6, 2, 1, 2, 3, 7, 6, 3, 2, 1, 2, 3, 6
   How many page faults would occur for following replacement algorithms assuming one, two, three, four, five, six or seven frames? Remember that all frames are initially empty, so your first unique pages will all cost one fault each.
   1. LRU replacement.
   2. FIFO replacement.
   3. Optimal replacement.
5. Question.


1. Some systems provide file sharing by maintaining a single copy of a file; other systems maintain several copies, one for each of the users sharing the file. Discuss the relative merits of each approach.
2. Compare the performance of C-SCAN and SCAn scheduling, assuming a uniform distribution of requests. Consider the average response time, the variation in response time and the affective band-width. How does performance depend on relative size of seek time and rotational latency
6. Question.


1. Describe three circumstances under which blocking I/O should be used. Describe three circumstances under which non-blocking I/O should be used. Why not just implement non-blocking I/O and have process busy-wait until their device is ready?
2. The list of all passwords is kept within the operating system. Thus, if a user manages to read this list, password protection is no longer provided. Suggest a scheme that will avoid this problem.
7. Question.


1. Under which circumstances would a client prefer a location-transparent DFS? Under which he/she prefers a location-independent DFS? Discuss the reasons for these preferences
2. Your company is building a computer network and you are asked to write an algorithm for achieving distributed mutual exclusion, which scheme will you use. Explain your choice.
8. Question.


1. The Linux kernel does not allow paging out kernel memory. What effect does this restriction have on kernel desing? What are two advantages and two disadvantages of this design decision?
2. The Windows 2000 VM manager uses a two-stage process to allocate memeory. Identify several ways in which this approach is benefial.