A Data Source Name (DSN) is the logical name that is used by Open Database Connectivity (ODBC) to refer to the drive and other information that is required to access data. The name is use by Internet Information Services for a connection to an ODBC data source, such as a Microsoft SQL Server database. To set this name, use the ODBC tool in Control Panel.
When you use an ODBC DSN entry to store the connection string values externally, you simplify the information that is needed in the connection string. This makes changes to the data source completely transparent to the code itself.
Make sure that you create a system DSN. ActiveX Data Objects (ADO) does not recognize user (or local) DSNs. Because they store settings in the registry, system DSNs offer slightly faster performance than file DSNs, which store connection parameters in a file on your hard disk.