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 input/output (I/O) requests made at different instants of time directed at a hypothetical disk having 200 tracks as given in the following table.

Assume that:
Current head position is at track no. 65
Direction of last movement is towards higher numbered tracks
Current clock time is 160 milliseconds
Head movement time per track is 1 millisecond.

“look” is a variant of “SCAN” disk-arm scheduling algorithm. In this algorithm, if no more I/O requests are left in current direction, the disk head reverses its direction. The seek times in Shortest Seek First (SSF) and “look” disk-arm scheduling algorithms respectively are:
a. 144 and 123 milliseconds
b. 143 and 123 milliseconds
c. 149 and 124 milliseconds
d. 256 and 186 milliseconds
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Answer: (b).143 and 123 milliseconds

82. A system contains 10 units of resource of same type. The resource requirement and current allocation of these resources for three processes P, Q and R are given below.Consider the following resource requests :

(i) P makes a request for 2 resource units.
(ii) Q makes request for 2 resources units.
(iii) R makes a request of 2 resource units.

For a safe state, which of the following options must be satisfied ?
safe state
a. Only request (i)
b. Only request (ii)
c. Only request (iii)
d. Request (i) and (ii)
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Answer: (c).Only request (iii)

83. Consider the following set of processes with the length of CPU burst time in milliseconds (ms).Assume that processes are stored in ready queue in following order :
A – B – C – D – E

Using round robin scheduling with time slice of 1 ms, the average turn around time is
round robin scheduling
a. 8.4 ms
b. 12.4 ms
c. 9.2 ms
d. 9.4 ms
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Answer: (a).8.4 ms

84. Consider a main memory with 3 page frames for the following page reference string :

5, 4, 3, 2, 1, 4, 3, 5, 4, 3, 4, 1, 4

Assuming that the execution of process is initiated after loading page 5 in memory, the number of page faults in FIFO and second chance replacement respectively are
a. 8 and 9
b. 10 and 11
c. 7 and 9
d. 9 and 8
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Answer: (d).9 and 8

85. A virtual memory based memory management algorithm partially swaps out a process. This is an example of
a. short term scheduling
b. long term scheduling
c. medium term scheduling
d. mutual exclusion
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Answer: (c).medium term scheduling

86. Assuming that the disk head is located initially at 32, find the number of disk moves required with FCFS if the disk queue of I/O block requests are 98, 37, 14, 124, 65, 67:
a. 310
b. 324
c. 320
d. 321
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Answer: (d).321

87. Let the page fault service time be 10 millisecond(ms) in a computer with average memory access time being 20 nanosecond(ns). If one page fault is generated for every 106 memory accesses, what is the effective access time for memory?
a. 21 ns
b. 23 ns
c. 30 ns
d. 35 ns
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Answer: (c).30 ns

88. Match the following:

a. RAID 0          i. Bit interleaved parity
b. RAID 1          ii. Non redundant stripping
c. RAID 2           iii. Mirrored disks
d. RAID 3          iv. Error correcting codes

Codes:
      a   b   c    d
a. iv   i    ii    iii
b. iii   iv   i    ii
c. iii   i    iv   ii
d. None of the above
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Answer: (d).None of the above

89. Consider the following processes with time slice of 4 milliseconds (I/O requests are ignored):

Process               A         B         C         D
Arrival time        0          1          2          3
CPU cycle         8          4          9          5

The average turn around time of these processes will be
a. 19.25 milliseconds
b. 18.25 milliseconds
c. 19.5 milliseconds
d. 18.5 milliseconds
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Answer: (b).18.25 milliseconds

90. A job has four pages A, B, C, D and the main memory has two page frames only. The job needs to process its pages in following order:

ABACABDBACD

Assuming that a page interrupt occurs when a new page is brought in the main memory, irrespective of whether the page is swapped out or not. The number of page interrupts in FIFO and LRU page replacement algorithms are
a. 9 and 7
b. 7 and 6
c. 9 and 8
d. 8 and 6
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Answer: (c).9 and 8

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