Operating System-Unix [3i Infotech Placement]: Sample Questions 71 - 73 of 78

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Question 71

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Describe in Detail

Essay▾

In Unix “. profile” files contains

Explanation

“. profile” contains commands meant to be executed only once in a session.

Bellow is the information that it includes:

  • The type of terminal user is using
  • A list of directories in which to locate the commands
  • A list of variable affecting the look and feel of our terminal
The Information

Question 72

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Essay▾

What are conditions for a machine to support Demand Paging?

Explanation

  • The process of mapping a large address space into a relatively small amount of physical memory is known as demand paging.
  • Demand paging is done by implementing ‘backing store’ .

Condition Required for Demand Paging:

  • Page based memory architecture.
  • Restartable instructions supported by the machine.
  • To start process, load the code page where the process will start executing.
  • Process references memory outside of loaded page, bring in as necessary.
  • Only brings page into main memory when a reference is made to a location on the page.
  • The characteristic problem is that there are many page faults when process is first started.

Question 73

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Describe in Detail

Essay▾

What do you mean by nice value?

Explanation

  • Nice value is the value that controls the priority of the process.
  • Value is returned by the nice () system call.
  • The equation for using nice value is Priority = ( “recent CPU usage” /constant) + (base-prriority) + (nice value)
  • Only the administrators can supply the nice value.
  • The nice () system call works for the running process only.
  • Nice value of one process cannot affect the nice value of the other process.
  • It is an integer value between 0 and 39.
  • The default nice value is 20.
  • Increasing this value decreases the priority.

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