Operating System-Unix [3i Infotech Placement]: Sample Questions 19 - 20 of 78

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Question 19


Describe in Detail


What is called a page fault?


Understanding of Page Fault
  • When a process access a page that is not a part of its working set or is not present in the main memory, a page fault occurs.
  • Operating system looks at an internal table to decide:
    • Invalid reference
    • Just not in memory
  • A major fault occurs when disk access is required.
  • A minor fault occurs due to page allocation.

Example: on start of application called such as “Chrome” .

  • The linux kernel searches in the physical memory and CPU cache for all the executables
  • When these are not found they have to be loaded from the disk causing page faults.

Question 20


Write in Short

Short Answer▾

What do you mean by the protection fault?


  • Protection fault happens when a process accesses the page for which it does not have the access permission.
  • This means that the process is accessing a region in RAM outside its assigned storage area-the operating system typically requires that the task or application be closed.
  • For example, a process incurs the protection fault when it attempts to write a page whose copy on write bit was set during the fork () system call.

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