title: What data type is GUID in SQL server?
body: <p>How is GUID internally stored and compared by SQL (particularly MS SQL server 2008)? Is it a number or string? Also, is there a big performance hit when using GUID as primary key? </p>
  
  <p>Besides the problem with clustering mentioned here: 
  <a href="https://stackoverflow.com/questions/11938044/guid-as-primary-key-best-practices">What are the best practices for using a GUID as a primary key, specifically regarding performance?</a></p>
  
  <p>I think it should be 128bit number (as described <a href="http://blogs.msdn.com/b/oldnewthing/archive/2008/06/27/8659071.aspx" rel="nofollow noreferrer">here</a>), but I cannot find mode details on how is it implemented in SQL server.</p>