A directory of Objective Type Questions covering all the Computer Science subjects. Here you can access and discuss Multiple choice questions and answers for various compitative exams and interviews.

61. An operating system supports a paged virtual memory, using a central processor with a cycle time of one microsecond. It costs an additional one microsecond to access a page other than the current one. Pages have 1000 words, and the paging device is a drum that rotates at 3000 revolutions per minute and transfers one million words per second. Further, one percent of all instructions executed accessed a page other than the current page. The instruction that accessed another page, 80% accessed a page already in memory and when a new page was required, the replaced page was modified 50% of the time. What is the effective access time on this system, assuming that the system is running only one process and the processor is idle during drum transfers ?
a. 30 microseconds
b. 34 microseconds
c. 60 microseconds
d. 68 microseconds
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Answer: (b).34 microseconds

62. 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

Which of the following options, gives the correct number of page faults related to LRU, FIFO, and optimal page replacement algorithms respectively, assuming 05 page frames and all frames are initially empty ?
a. 10, 14, 8
b. 8, 10, 7
c. 7, 10, 8
d. 7, 10, 7
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Answer: (b).8, 10, 7

63. Consider a file currently consisting of 50 blocks. Assume that the file control block and the index block is already in memory. If a block is added at the end (and the block information to be added is stored in memory), then how many disk I/O operations are required for indexed (single-level) allocation strategy ?
a. 1
b. 101
c. 27
d. 0
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Answer: (a).1

64. A virtual memory has a page size of 1K words. There are eight pages and four blocks. The associative memory page table contains the following entries. Which of the following list of virtual addresses (in decimal) will not cause any page fault if referenced by the CPU?
virtual memory
a. 1024, 3072, 4096, 6144
b. 1234, 4012, 5000, 6200
c. 1020, 3012, 6120, 8100
d. 2021, 4050, 5112, 7100
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Answer: (c).1020, 3012, 6120, 8100

65. Suppose that the number of instructions executed between page faults is directly proportional to the number of page frames allocated to a program. If the available memory is doubled, the mean interval between page faults is also doubled. Further, consider that a normal instruction takes one micro second, but if a page fault occurs, it takes 2001 micro seconds. If a program takes 60 sec to run, during which time it gets 15000 page faults, how long would it take to run if twice as much memory were available?
a. 60 sec
b. 30 sec
c. 45 sec
d. 10 sec
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Answer: (c).45 sec

66. Consider a disk with 16384 bytes per track having a rotation time of 16 msec and average seek time of 40 msec. What is the time in msec to read a block of 1024 bytes from this disk?
a. 57 msec
b. 49 msec
c. 48 msec
d. 17 msec
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Answer: (b).49 msec

67. A system has four processes and five allocatable resources. The current allocation and maximum needs are as follows.The smallest value of x for which the system in safe state is .............
safe state of system
a. 1
b. 3
c. 2
d. None of the above
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Answer: (d).None of the above

68. Match the following with respect to various memory management algorithms :

List - I                                     List - II
(a) Demand paging                 (i) degree of multiprogramming
(b) Segmentation                     (ii) working set
(c) Dynamic partitions             (iii) supports user view of memory
(d) Fixed partitions                  (iv) compaction

Codes :
      (a)  (b)   (c)  (d)
a. (iii)  (iv)  (ii)   (i)
b. (ii)  (iii)   (i)   (iv)
c. (iv) (iii)  (ii)   (i)
d. (ii)  (iii)  (iv)  (i)
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Answer: (d).(ii)  (iii)  (iv)  (i)

69. Function of memory management unit is :
a. Address translation
b. Memory allocation
c. Cache management
d. All of the above
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Answer: (a).Address translation

70. Consider a system with twelve magnetic tape drives and three processes P1, P2 and P3. Process P1 requires maximum ten tape drives, process P2 may need as many as four tape drives and P3 may need upto nine tape drives. Suppose that at time t1, process P1 is holding five tape drives, process P2 is holding two tape drives and process P3 is holding three tape drives. At time t1, system is in:
a. safe state
b. unsafe state
c. deadlocked state
d. starvation state
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Answer: (b).unsafe state

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