Basic CS-Operating System [3i Infotech Placement]: Sample Questions 82 - 83 of 89

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Question 82

Operating System
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Describe in Detail

Essay▾

What is a semaphore?

Explanation

Understanding of Semaphore
  • A semaphore controls access by multiple processes to a common resource in a parallel programming environment.
  • Widely used to control access to files and shared memory.
  • Functionalities associated with semaphores are set, check and wait until it clears to set it again.
  • The two most common kinds of semaphores are counting semaphores and binary semaphores.
  • Counting semaphores take non-negative integer values and binary semaphore can take the value only.
  • Semaphores are commonly used for two purposes: to share a common memory space and to share access to files.

Question 83

Operating System
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Describe in Detail

Essay▾

What is FtDisk?

Explanation

  • FtDisk is fault tolerant disk driver for NT which provides several ways to combine multiple SCSI disk drives into one logical volume.
  • Its special property is that it can continue operating under failure of some of parts.
    • If operating quality decreases, the decrease is proportional to the failure.
    • Provides high availability for life critical systems.
  • Uses a hardware technique called sector sparing and NTFS uses a software technique called cluster remapping.

Fault Tolerance is Achieved by Many Techniques

  • Fault masking:
    • Process that prevents faults from introducing error.
  • Reconfiguration:
    • Process of isolating and eliminating faulty components from a system and restoring the system.

Advantages:

  • Higher reliability
  • Lower total cost
  • Psychological worry free use.

Disadvantages:

  • Cost of redundancy

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