GATE CSE 2025 | Set 1 | Question: 44

Question

In optimal page replacement algorithm, information about all future page references is available to the operating system (OS). A modification of the optimal page replacement algorithm is as follows:

The OS correctly predicts only up to next $4$ page references (including the current page) at the time of allocating a frame to a page.

A process accesses the pages in the following order of page numbers:
$$1,3,2,4,2,3,1,2,4,3,1,4$$
If the system has three memory frames that are initially empty, the number of page faults that will occur during execution of the process is __________. (Answer in integer)

Comments

Including current is the ...very page we are about to reference...eg 132 are in memory now page 4 is about to. Be referenced so we look for all pages after  4 for their future references but here OS predicts only four reference correctly including current ie 4 so next 3 reference after 4 is counted

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@jacknroll @SilentClimber 2026 was vice versa ☺

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I had set1 in both time

Answer 1

       $\text{page fault: ✔}$

       $\text{ page hit :  ✘}$

Answer 2

6 page faults.

Answer 3

HERE IS THE SIMPLE AND DETAILS EXPLANATION 

Answer 4

Page fault =6