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.

21. Consider the following justifications for commonly using the two-level CPU scheduling :

I. It is used when memory is too small to hold all the ready processes.

II. Because its performance is same as that of the FIFO.

III. Because it facilitates putting some set of processes into memory and a choice is made from that.

IV. Because it does not allow to adjust the set of in-core processes.

Which of the following is true?
a. I, III and IV
b. I and II
c. III and IV
d. I and III
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Answer: (d).I and III

22. For the implementation of a paging scheme, suppose the average process size be x bytes, the page size be y bytes, and each page entry requires z bytes. The optimum page size that minimizes the total overhead due to the page table and the internal fragmentation loss is given by
a. x/2
b. xz/2
c. √2xz/2
d. √xz/2
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Answer: (a).x/2

23. Which methods are utilized to control the access to an object in multi-threaded programming?
a. Asynchronized methods
b. Synchronized methods
c. Serialized methods
d. None of the above
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Answer: (a).Asynchronized methods

24. Various storage devices used by an operating system can be arranged as follows in increasing order of accessing speed:
a. Magnetic tapes → magnetic disks → optical disks →  electronic disks →  main memory →  cache →  registers
b. Magnetic tapes → magnetic disks → electronic disks → optical disks → main memory → cache → registers
c. Magnetic tapes → electronic disks → magnetic disks → optical disks → main memory → cache → registers
d. Magnetic tapes → optical disks → magnetic disks →electronic disks →  main memory → cache → registers
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Answer: (c).Magnetic tapes → electronic disks → magnetic disks → optical disks → main memory → cache → registers

25. How many disk blocks are required to keep list of free disk blocks in a 16 GB hard disk with 1 kB block size using linked list of free disk blocks? Assume that the disk block number is stored in 32 bits.
a. 1024 blocks
b. 16794 blocks
c. 20000 blocks
d. 1048576 blocks
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Answer: (d).1048576 blocks

26. Consider an imaginary disk with 40 cylinders. A request come to read a block on cylinder 11. While the seek to cylinder 11 is in progress, new requests come in for cylinders 1, 36, 16, 34, 9 and 12 in that order. The number of arm motions using shortest seek first algorithm is
a. 111
b. 112
c. 60
d. 61
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Answer: (d).61

27. An operating system has 13 tape drives. There are three processes PI, P2 & P3.1 Maximum requirement of PI is 11 tape drives, P2 is 5 tape drives and P3 is 8 tape drives. Currently, PI is allocated 6 tape drives, P2 is allocated 3 tape drives and P3 is allocated 2 tape drives. Which of the following sequences represent a safe state?
a. P2 P1 P3
b. P2 P3 P1
c. P1 P2 P3
d. P1 P3 P2
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Answer: (a).P2 P1 P3

28. Monitor is an Interprocess Communication (IPC) technique which can be described as
a. It is higher level synchronization primitive and is a collection of procedures, variables, and data structures grouped together in a special package
b. It is a non-negative integer which apart from initialization can be acted upon by wait and signal operations
c. It uses two primitives, send and receive which are system calls rather than language constructs
d. It consists of the IPC primitives implemented as system calls to block the process when they are not allowed to enter critical region to save CPU time
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Answer: (d).It consists of the IPC primitives implemented as system calls to block the process when they are not allowed to enter critical region to save CPU time

29. A disk drive has 100 cylinders, numbered 0 to 99. Disk requests come to the disk driver for cylinders 12,26,24,4,42,8 and 50 in that order. The driver is currently serving a request at cylinder 24- A seek takes 6 msec per cylinder moved. How much seek time is needed for shortest seek time first (SSTF) algorithm ?
a. 0.984 sec
b. 0.396 sec
c. 0.738 sec
d. 0.42 sec
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Answer: (d).0.42 sec

30. Let Pi and Pj be two processes, R be the set of variables read from memory, and W be the set variables written to memory. For the concurrent execution of two processes Pi and Pj, which of the following conditions is not true?
a. R(Pi) ∩ W (Pj) = Φ
b. W(Pi) ∩ R (Pj) = Φ
c. R(Pi) ∩ R (Pj) = Φ
d. W(Pi) ∩ W (Pj) = Φ
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Answer: (c).R(Pi) ∩ R (Pj) = Φ

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