Balanced Technology eXtended (BTX)
 

When Intel released the BTX standard in 2003, ATX was going stronger then ever. We are now at a point of where ATX is hitting a limit on thermal design. Ducting can only do so much for us. It is time to move on to a new and better standard. Enter BTX...

Link: http://www.aselabs.com/articles.php?id=166