JUNE 1998

Question Paper of CS-13 – Operating Systems of June 1998 from IGNOU

Time : 3 Hours
Max. Marks : 75

Note: Question 1 is compulsory.
Answer any three from the rest.

1.
(a) Identify and discuss all operations and parameters that influence the effective memory access time in a virtual-memory system. Indicate the most significant changes that may be expected with future technological improvements, such as introduction of the secondary storage devices with access time one or more orders of magnitude faster than that of contemporary devices.

(b) A disk has 305 cylinders, four heads and 17 sectors of 512 bytes each per track. The disk is rotated at 3000 rpm and it has a moving head assembly with an average head positioning time of 30 ms. The peak date transfer rate that the drive can sustain is 4 mbps. Calculate the best and the worst case time needed to transfer 20 consecutive and 20 randomly distributed blocks (sectors)from such a disk. Indicate the dominant factors in determining the transfer times and the variability between the best case and the worst case figures.

(c) Give several reasons why the study of concurrency is appropriate in OS design

2.
(a) Write a program/algorithm that solves the readers and writers problem solved with conditional critical regions.

(b) Compare and contrast the semaphore to the same problem(2(a)) in terms of data abstraction and readability of the code

3. Describe the function of a translation lookaside buffer (TLB) in a paging system and discuss the issues and operations involved in TLB management in OS. In particular, discuss the options and trade-off in TLB entry allocation and replacement policies. Indicate which of these operations are time-critical and therefore suitable candidates for implementation in hardware.

4.
(a) Discuss the basic model of cryptography.

(b) Discuss the Data Encryption Standard (DES) algorithm. What are its limitations.

5. Discuss processor management and scheduling in multiprocessor operating system design.

6.
(a) Discuss the complexities involved in interprocess communication and synchronization in a distributed system compared to a centralized system.

(b) Explain the algorithm for election of a successor in a distributed system. Also discuss the correctness and performance of the algorithm.

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