Microsoft has changed the edition structure for SQL Server 2008 R2 by adding two new editions: Datacenter and Parallel Data Warehouse. The Datacenter edition adds features for management improvement and support for more than 8 processors. The Parallel Data Warehouse edition supports much larger data stores and enhanced data warehouse functions. For more information about these new editions and the traditional editions and what they'll look like in SQL Server 2008 R2, visit this page:
http://www.microsoft.com/sqlserver/2008/en/us/R2-editions.aspx
