title: Confusion about a practical example of FIFO Page Replacement Algorithm?
body: <p>I'm doing some theoretical examples with different page replacement algorithms, in order to get a better understanding for when I actually write the code. I'm kind of confused about this example.</p>
  <blockquote>
  <p>Given below is a physical memory with 4 tiles (4 sections?). The following pages are visited one after the other:</p>
  <p><code>R = 1, 2, 3, 2, 4, 5, 3, 6, 1, 4, 2, 3, 1, 4</code></p>
  <p>Run  the FIFO page replacement algorithm on R with 4 tiles.</p>
  </blockquote>
  <p>I know that  when a page needs to be swapped in, the operating system swaps out the page which has been in the memory for the longest period of time. In practice I'll have:</p>
  <pre><code>Time    1 2 3 4 5 6 7 8 9 10 11 12 13 14
  Page    1 2 3 2 4 5 3 6 1 4  2  3  1  4
  Tile 1  1 1 1 1 1 5 5
  Tile 2    2 2 2 2 2 2
  Tile 3      3 3 3 3 3
  Tile 4          4 4 4
  </code></pre>
  <p>I'm not sure what happens at time = 8. I know that it won't replace page 5 and 4, but I'm not sure between 3 and 2. Since at time = 4 we have a 2, does it mean that page 3 will be replaced? Or is it that, since at time = 4, we already had 2 in the memory, therefore at time = 8 we replace 2?</p>