Are you thinking of writing database applications for a mobile device or Smartphone? If so, you might want to look into Microsoft SQL Server Compact 3.5. SQL Server Compact is a very small (under 2MB of RAM) database that runs on Windows server and desktop OSs as well as Windows Mobile devices. You can check out SQL Server Compact 3.5 at http://www.microsoft.com/sql/editions/compact/default.mspx.