title: Difference between three tier vs. n-tier
body: <p>I just came across the following sentence:</p>
  
  <blockquote>
    <p>As the industry has moved from a three
    tier model to n-tier models, the object relational impedance mismatch has become more prevalent.</p>
  </blockquote>
  
  <p>But I can't find a concise explanation of the difference between three tier and n-tier. I know what three tier is, and I assume n-tier just adds one or more tiers. I'm just not sure what these additional tiers would be. If anyone has a short explanation or simply a good link, that would be much appreciated.</p>