title: Virtually indexed physically tagged cache Synonym
body: <p>I am not able to entirely grasp the concept of synonyms or aliasing in VIPT caches.</p>
  
  <p>Consider the address split as:-</p>
  
  <p><a href="https://i.stack.imgur.com/TxF9z.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/TxF9z.png" alt="enter image description here"></a></p>
  
  <p>Here, suppose we have 2 pages with different VA's mapped to same physical address(or frame no).</p>
  
  <p>The <strong>pageno part of VA</strong> (bits 13-39) which are different gets translated to <strong>PFN of PA</strong>(bits 12-35) and the PFN remains same for both the VA's as they are mapped to same physical frame.</p>
  
  <p>Now the <strong>pageoffset</strong> part(bits 0-13) of both the VA's are same as the data which they want to access from a particular frame no is same.</p>
  
  <p>As the <strong>pageoffset part of both VA's are same</strong>, bits (5-13) will also be same, so the <strong>index or set no is the same</strong> and hence there should be <strong>no aliasing</strong> as only single set or index no is mapped to a physical frame no.</p>
  
  <p>How is bit 12 as shown in the diagram, responsible for aliasing ? I am not able to understand that.</p>
  
  <p>It would be great if someone could give an example with the help of addresses.</p>
  
  <p>Thanks . </p>