Microsoft SQL Server 2012 Express Edition is a great database engine that is more than capable of handling most small business database requirements. There are however some limitations. The details below outline the main limitations in SQL 2012 Express Edition.
1 CPU (based on a socket) or 4 cores.
The lesser of the two is used.
If you have 1 CPU that contains 8 cores, it will only use 4 cores.
If you have a system with 2 dual core CPU’s, it will only use 2 cores (from the 1 CPU socket as that’s the lesser of the two).
Maximum of 1GB for the database engine.
(Note: SQL 2012 Express Edition with Advanced Services includes reporting features, and has a limit of 4GB for the reporting services. It still has a 1GB limit for the database engine).
The maximum database size is 10GB.
For a full rundown of the features that each SQL 2012 editions have included, you can visit http://msdn.microsoft.com/en-us/library/cc645993(v=SQL.110).aspx