ODBC

The Microsoft Open Database Connectivity (ODBC) interface is a C programming language interface that makes it possible for applications to access data from a variety of database management systems (DBMSs). A central connection route is set up, called a System DSN, through which many connections can be made to the same data source.

However, it is becoming widely accepted that this is not the most efficient connection method. In fact, this type of connection is slightly less efficient than using a DSN-less connection (ADO connect string), because using a DSN means that each database connection requires a registry lookup. This registry lookup is not overly expensive, but it does add up when you have a number of concurrent users (more than 10 concurrent connections using a DSN begins to cause an overhead).