title: What type of B-trees is actually used in SQL Server indices?
body: <p>Many books on SQL Server and even <a href="http://msdn.microsoft.com/en-us/library/ms190457.aspx" rel="nofollow noreferrer">BOL</a> mention that SQL Server uses <a href="http://en.wikipedia.org/wiki/B-tree" rel="nofollow noreferrer">B-tree</a> to store indices. Recently I have learnt from the lecture on indices that <a href="http://en.wikipedia.org/wiki/B%2B_tree" rel="nofollow noreferrer">B+ trees</a> are actually used.</p>
  <p>Now I am totally confused.</p>
  <p>To sum up:
  Could you please give exact definition of B and B+ tree?
  Please do it in plain English and if you are referring to other entities, please define those too.
  And last but not least, what type of B-trees is used in SQL Server indices?</p>