title: What is the "FS"/"GS" register intended for?
body: <p>So I know what the following registers and their uses are supposed to be:</p>
  
  <ul>
  <li><p>CS = Code Segment (used for IP)</p></li>
  <li><p>DS = Data Segment (used for MOV)</p></li>
  <li><p>ES = Destination Segment (used for MOVS, etc.)</p></li>
  <li><p>SS = Stack Segment (used for SP)</p></li>
  </ul>
  
  <p>But what are the following registers intended to be used for?</p>
  
  <ul>
  <li><p>FS = "File Segment"?</p></li>
  <li><p>GS = ???</p></li>
  </ul>
  
  <p>Note: I'm <strong>not</strong> asking about any particular operating system -- I'm asking about what they were intended to be used for by the CPU, if anything.</p>