Test Series Question on Second Chance page Replacement

Question

Demand paging uses a second chance page replacement policy (clock). It uses one use bit to give every page one more chance in FIFO replacement. Whenever a page is referenced its use bit set to 0. Whenever it is need to replace by other page for the first time then its use bit is changed to 1 and next page will be searched for replacement. If already given the chance then it will be replaced.
Assume that the system has 3 page frames. Consider the following page reference stream in the given order.
                                                              7, 0, 1, 2, 0, 3, 0, 4, 2, 3
The number of page faults occur using clock algorithm are ___________.

Comments

Is this in GATE syllabus ?? Or any chance of coming in GATE ?

Answer 1

Considering, when new page read into a memory frame has the second chance bit set to ZERO (0) and Each time a memory frame is referenced, set the "second chance" bit to ONE (1) - this will give the frame a second chance.

Here, PF = Page Fault, SC = Second Chance

So, Total Page Fault is 8. 

Comments

whenever a page is read into memory,or referenced ,it's use bit is set to 0.During replacement process it's use bit is set 1,if it is 0 or replaced by the current page if it is already 1.

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Bhai...

Ans is 7 Page Faults Bhai....

 

When page number 4 is entering, it needs to replace page number 0 which is in 2nd frame but we can't replace it because 0 page has reference bit 1 so we are giving it a second chance to change its reference bit to 0 and then the page 4 replaces 2 page no. 2(as it has reference bit 0) which is in 1st frame

Answer 2

7-0  7-0  7-0   2-0   2-0  2-0   2-0   4-0   4-0   4-0
       0-0  0-0   0-0   0-1  0-0   0-1   0-0   2-0    2-0
              1-0   1-0   1-0  3-0   3-0   3-0   3-0    3-1
M     M    M     M      H    M      H     M     M      H

Threrfore 7 page fault.

Comments

In 4th step, when 2 is on i/p, shouldn't use bits of 7,0,1 be set to 1 first, then 7 be replaced (already given a chance) with 2 : resulting in 0-1 1-1 2-0 ?

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i dont know.
i learned second chance algo  this way.

Answer 3

I am getting 7 as answer.