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PREVIOUS YEAR SOLVED PAPERS - August 2016 Paper 3

Avatto > > UGC NET COMPUTER SCIENCE > > PREVIOUS YEAR SOLVED PAPERS > > August 2016 Paper 3

51. 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?

  • Option : B
  • Explanation :
    Effective access time = 0.99 * (1 µs) + 0.8 *.02 µs + 0.001 * ( 10000 µs + 1000 µs) + 0.001 * (20000 µs + 2000 µs) = (0.99 +0.016+22.0+11.0) µs = 34 µs So, option (B) is correct.
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52. 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 ?

  • Option : B
  • Explanation :
    In LRU:

    In FIFO:

    In Optimal:

    Respectively there are 8, 10, 7 page faults. So, option (B) is correct.
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53. 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?

  • Option : A
  • Explanation :
    According to question file control block and the index block is already in memory. So, we don't need to transfer them from anywhere else for further operation. If a block is added at the end (and the block information to be added is stored in memory), this is a single operation. So we need only one I/O operation required for indexed (single-level) allocation strategy. So, option (A) is correct.
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54. Given the following two languages :
L1 = {uwwRν | u, v, w ∈ {a, b}+}
L2 = {uwwRν | u, ν, w ∈ {a, b}+, |u| > |ν|}
Which of the following is correct ?

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55. An experimental file server is up 75% of the time and down for 25% of the time due to bugs. How many times does this file server have to be replicated to give an availability of at least 99% ?

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August 2016 Paper 3