LRU Apprx.: Second-Chance Algorithm
Second-Chance algorithm is actually a FIFO replacement algorithm with a small modification that causes it to approximate LRU.
When a page is selected according to a FIFO order, we check its reference bit. If it is set (the page was referenced), we clear it and look for another page.
Also called the clock algorithm.
In the worst case, when all bits are set, the pointer cycles through all of the pages, giving each page a second chance and clearing its bit.
Requires hardware support for reference bit.