title: How to Calculate Effective Access Time
body: <p>Assume TLB hit ratio is 90%, physical memory access takes 100ns, TLB access takes 20 ns, compute the effective access time for a processor that uses two level page tables, and parallel TLB and page table indexing.</p>
  
  <p>This was my formula: </p>
  
  <pre><code>(H)(TLB access time + mem access time) + (1-H)(TLB access + PT access + mem access)
  </code></pre>
  
  <p>This was my calculation:</p>
  
  <pre><code>EAT = [(.90) * (100ns + 20ns) + (1-.90)(20ns + 100ns*2 + 100ns)] = 130ns
  </code></pre>
  
  <p>I understand 2* 100ns because of the two-level page table, my confusion was when my professor said the TLB access time 20ns should not be included within the miss calculation. </p>
  
  <p>Could someone please explain the reasoning behind this?</p>