Working Set Model

Question

Consider a system uses working-set model for frame allocations. Working-set window size is 7. Following is sequence of virtual page references:

5, 4, 3, 3, 4, 1, 2, 2, 1, 2, 1, 1, 5, 4, 3, 5

What will be the minimum number of elements in a working set on execution of the above sequence?

The question is from test series. Here according to their solution minimum number of elements will be 2.

But I think that after executing the above sequence in the beginning the working set will contain only frame 5 so the minimum number of elements will be 1.

 

Answer 1

You have to check after  completely filling the window size (here it is 7)

so in the process of adding new element to the working set window and swapping out the first one from the left.

you will get  |1|2|2|1|2|1|1|   here only two distinct elements are present that’s why 

minimum number of elements in a working set on execution of the above sequence = 2.

Answer 2

no, 

working set window means how many pages are there actively used together. There are page references it's different from other page replacement algorithm.

it's asked in question that in working set minimum number of elements means you will have to check in window size 7.