Difference Between Sqlserver2008 and Sqlserver2008R2

SQL 2008 R2 Express is the latest version, it could has been called
something like SQL-2008 Express Service Pack 2 or SQL 2010 Express but they
have chosen to call it SQL 2008 R2 Express. Beside some bugs that have been
corrected, the main new feature of this release is the maximum size of a
database that has been increased from 4Gigs to 10Gigs. All the other
limitations have remained the same.