Basic CS-Operating System [3i Infotech Placement]: Sample Questions 2 - 3 of 89

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Question 2

Operating System



When a bicycle is in motion, the force of friction exerted by the ground on the two wheels is such that it acts


Choice (4)


In the forward direction on the front wheel and in the backward direction on the rear wheel.


In the backward direction on both the front and rear wheels.


In the backward direction on the front wheel and in the forward direction on the rear wheel.


Question does not provide sufficient data or is vague




  • Pedalling the bicycle merely rotates the back wheel in clockwise sense.
  • The velocity of point of contact is therefore backwards, so, friction must act forward on the rear wheel.
  • This frictional force causes a translational acceleration of the entire bicycle, including the front wheel.
  • The velocity of point of contact tends to develop in the forward direction so friction acts in the backward direction.

Similar reasoning applies to a car, for the engine merely rotates the back wheel.

Question 3

Operating System

Describe in Detail


What are local and global page replacements?


Global and Local Allocation

Local Replacement

  • An incoming page is brought in only to the relevant process address space.
  • Considers every process individually.
  • Adjusts memory allocation according to relative importance of each process to improve performance.
  • Local replacement is done for one process and one process only.
  • Does not allow a process to replace page in another processes memory

Global Replacement

  • Policy allows any page frame from any process to replace any other page (even page of another process) .
  • The latter is applicable to variable partitions model only.
  • Applied to every process unit.
  • Ignore characteristics of individual process behaviour- aims to achieve the best overall performance.

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