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.

81. Consider the situation in which the disk read/write head is currently located at track 45 (of tracks 0-255) and moving in the positive direction. Assume that the following track requests have been made in this order: 40, 67, 11, 240, 87. What is the order in which optimized C-SCAN would service these requests and what is the total seek distance?
a. 600
b. 810
c. 505
d. 550
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Answer: (c).505

82. Suppose the following disk request sequence (track numbers) for a disk with 100 tracks is given: 45, 20, 90, 10, 50, 60, 80, 25, 70. Assume that the initial position of the R/W head is on track 50. The additional distance that will be traversed by the R/W head when the Shortest Seek Time First (SSTF) algorithm is used compared to the SCAN (Elevator) algorithm (assuming that SCAN algorithm moves towards 100 when it starts execution) is _________ tracks.
a. 8
b. 9
c. 10
d. 11
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Answer: (c).10

83. Consider a disk pack with a seek time of 4 milliseconds and rotational speed of 10000 rotations per minute (RPM). It has 600 sectors per track and each sector can store 512 bytes of data. Consider a file stored in the disk. The file contains 2000 sectors. Assume that every sector access necessitates a seek, and the average rotational latency for accessing each sector is half of the time for one complete rotation. The total time (in milliseconds) needed to read the entire file is _________.
a. 14020
b. 14000
c. 25030
d. 15000
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Answer: (a).14020

84. Consider a typical disk that rotates at 15000 rotations per minute (RPM) and has a transfer rate of 50 × 106 bytes/sec. If the average seek time of the disk is twice the average rotational delay and the controller’s transfer time is 10 times the disk transfer time, the average time (in milliseconds) to read or write a 512 byte sector of the disk is _____________.
a. 6.2
b. 6.1
c. 6.0
d. 5.9
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Answer: (b).6.1

85. Consider a disk queue with requests for I/O to blocks on cylinders 47, 38, 121, 191, 87, 11, 92, 10. The C-LOOK scheduling algorithm is used. The head is initially at cylinder number 63, moving towards larger cylinder numbers on its servicing pass. The cylinders are numbered from 0 to 199. The total head movement (in number of cylinders) incurred while servicing these requests is:
a. 346
b. 165
c. 154
d. 173
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Answer: (b).165

86. Which of the following DMA transfer modes and interrupt handling mechanisms will enable the highest I/O band-width?
a. Transparent DMA and Polling interrupts
b. Cycle-stealing and Vectored interrupts
c. Block transfer and Vectored interrupts
d. Block transfer and Polling interrupts
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Answer: (c).Block transfer and Vectored interrupts

87. Consider three processes (process id 0, 1, 2 respectively) with compute time bursts 2, 4 and 8 time units. All processes arrive at time zero. Consider the longest remaining time first (LRTF) scheduling algorithm. In LRTF ties are broken by giving priority to the process with the lowest process id. The average turn around time is:
a. 13 units
b. 14 units
c. 15 units
d. 16 units
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Answer: (a).13 units

88. Consider three processes, all arriving at time zero, with total execution time of 10, 20 and 30 units, respectively. Each process spends the first 20% of execution time doing I/O, the next 70% of time doing computation, and the last 10% of time doing I/O again. The operating system uses a shortest remaining compute time first scheduling algorithm and schedules a new process either when the running process gets blocked on I/O or when the running process finishes its compute burst. Assume that all I/O operations can be overlapped as much as possible. For what percentage of time does the CPU remain idle?
a. 0%
b. 10.6%
c. 30.0%
d. 89.4%
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Answer: (b).10.6%

89. Consider three CPU-intensive processes, which require 10, 20 and 30 time units and arrive at times 0, 2 and 6, respectively. How many context switches are needed if the operating system implements a shortest remaining time first scheduling algorithm? Do not count the context switches at time zero and at the end.
a. 1
b. 2
c. 3
d. 4
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Answer: (b).2

90. Which of the following process scheduling algorithm may lead to starvation
a. FIFO
b. Round Robin
c. Shortest Job Next
d. None of the above
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Answer: (c).Shortest Job Next

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