What is the second chance algorithm?

The second chance algorithm is a page replacement policyIt is a policy that defnes which chunk of memory should be placed inside the disk. that uses a FIFOFirst In First Out algorithm and a hardware-provided reference bit. The page table is traversed in a FIFO (circular queue) manner. If a page table is found with its reference bit not set, then that page is selected as the next victim. If the next page in FIFO has its reference bit set, it's given a second chance. The reference bit is set to null, and the FIFO search continues. If some other page is found that had its reference bit not set, that page will be selected as the victim for page replacement, and the page given a second chance would remain in the page table.

If there are no other pages that do not have their reference bit set, then the page given a second chance will be selected as the next victim in the next round of page search.

The following illustrates the flow of the second chance algorithm:

Explanation

A bit is associated with each page. It's initially set to 0, and when the page is referenced, it's set to 1.

Starting from the current pointer, if there is a need to replace a page to bring a new frame, the reference bit is checked. If reference bit = 0, that page is replaced. Otherwise, the bit is set to 0, the page is left in the memory, and the pointer is incremented.

Algorithm

1. Create multiple arrays representing frames to track pages in memory and another boolean arrayArray that holds either true or false values. to track page access.

2. Start traversing the array. If the page is already present, set its corresponding boolean array element to true and return.

3. If the page doesn't exist, check whether the pointer pointing to the reference bit is null (this shows that the cache is not full). If the pointer is null, we'll insert the element at that position and return. Otherwise, we'll traverse the array and keep updating the corresponding reference bit to false until we find a bit already false and replace that page and return.

4. We output the page fault countIt is a count that decribes how many times virtual memory movement has occured to and from the disk..