Code: AC13 Subject: OPERATING SYSTEMS
Time: 3 Hours Max. Marks: 100
NOTE: There are 9 Questions in all.
· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.
· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.
· Any required data not explicitly given, may be suitably assumed and stated.
Q.1 Choose the correct or best alternative in the following: (2x10)
a. Programs that do not require interaction but require long execution times may be served well by
(A) Multiprogramming operating systems
(B) Time Sharing operating systems
(C) Batch operating systems
(D) Distributed operating systems
b. The structure of operating systems by removing all non-essential components from kernel, and implementing them as system and user-level programs is termed as
(A) Micro kernel (B) Monolithic kernel
(C) Macro kernel (D) Virtual kernel
c. Each process that wants to communicate must explicitly name the recipient or sender for communication. This type of mode is used in
(A) Asymmetric communication (B) Direct communication
(C) Buffering communication (D) Indirect communication
d. Round Robin(RR) scheduling is designed especially for
(A) Priority systems (B) FCFS systems
(C) Time Sharing systems (D) Interactive systems
e. Translation Look-aside Buffer (TLB) is used in
(A) Segmentation (B) Fragmentation
(C) Swapping (D) Paging
f. Once a file is declared as shared by its creator, it cannot be modified by others. This property is known as
(A) Access control file (B) Immutable shared file semantics
(C) Mutable shared file semantics (D) Andrew shared file semantics
g. Cycle stealing concept is used in
(A) DMA (B) Buffering
(C) Caching (D) Device reservation
h. If a process spends more time in paging than execution, CPU utilization decreases. This is known as
(A) Bashing (B) Caching
(C) Thrashing (D) Fetching
i. An example of Election Algorithm used in distributed systems is
(A) Bakery algorithm (B) Banker’s algorithm
(C) Best-fit algorithm (D) Bully algorithm
j. In dead lock prevention scheme using time-stamps, wait-die scheme is based on
(A) Preemptive technique (B) Non-preemptive technique
(C) Priority technique (D) Centralized scheme
Answer any FIVE Questions out of EIGHT Questions.
Each question carries 16 marks.
Q.2 a. Explain the functionality of each of the following and give their differences
(i) Short-term scheduler
(ii) Medium-term scheduler
(iii) Long-term scheduler components. (6)
b. List five services provided by an operating system. Explain how each provides convenience to the users. Explain also in which cases it would be impossible for user-level programs to provide these services. (10)
Q.3 a. Explain the following
(i) The efficiency and performance of disk usage. (2)
(ii) Block diagram of the following: (8)
(a) I/O without unified buffer (b) I/O with a unified buffer
b. Explain any two LRU approximation page replacements. (6)
Q.4 a. What is the meaning of the term busy waiting? What other kinds of waiting are there in an OS? Can busy waiting be avoided altogether? (8)
b. Give answers for the following:
(i) Consider a logical-address space of eight pages of 1,024 words each, mapped onto a physical memory of 32 frames. How many bits are there in the logical and physical addresses? (4)
(ii) Consider a paging system with the page table stored in memory.
(a) If a memory reference takes 200 nanoseconds, how long does a paged memory reference take?
(b) If we add associative registers, and 75 percent of all page-table references are found in the associative registers, what is the effective memory reference time? (Assume that finding a page-table entry in the associative registers takes zero time, if the entry is there.) (4)
Q.5 a. Explain various types of routing strategies used in distributed systems (4)
b. Suppose that a disk drive has 5,000 cylinders, numbered 0 to 4999. The drive is currently serving a request at cylinder 143, and the previous request was at cylinder 125. The queue of pending requests, in FIFO order, is
86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130
Starting from the current head position, what is the total seek 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) SSTF
(iii) SCAN (iv) LOOK
(v) C-SCAN (vi) C-LOOK (12)
Q.6 a. Explain the following
(i) Define streams and their importance. (2)
(ii) Draw block diagram to explain Inter Computer Communication between Sending system and Receiving system (6)
b. Explain various types of file directory structure with relevant diagram. (8)
Q.7 a. Many CPU scheduling algorithms are parameterized. For example, the RR algorithm requires a parameter to indicate the time slice. Multilevel feedback queues require parameters to define the number of queues, the scheduling algorithms for each queue, the criteria used to move processes between queues, and so on. These algorithms are thus really sets of algorithms (for example, the set of RR algorithms for all time slices, and so on). One set of algorithms may include another (for example, the FCFS algorithm is the RR algorithm with an infinite time quantum). What (if any) relation holds between the following pairs of sets of algorithms? (8)
(i) Priority and SJF (ii) Multilevel feedback queues and FCFS
(iii) Priority and FCFS (iv) RR and SJF
b. Suppose that a system is in an unsafe state. Taking a suitable example show that it is possible for the processes to complete their execution without entering dead lock state. (8)
Q.8 a. Compare Caching and Remote services used in distributed file systems. (8)
b. Explain the concept of atomicity used in Distributed communications. Explain two phase commit protocol and how two phase commit (2PC) responds to various types of failures. (2+6)
Q.9 a. Explain the following
(i) Explain various types of programming threats and system threats. (6)
(ii) Give any four methods to secure systems and facilities. (2)
b. Explain the following communication techniques used in Client-Server Systems (8)
(i) Remote Procedure Calls (RPC) (ii) Remote Method Invocation (RMI)