The early version of JDBC provided a Driver class with a GetConnection method for application. Underneath Driver uses Java Socket class to get a connection to the database. Later, DriverManager class provide the connection using an url. Using a generic interface saved the application the need to know which specific driver to use. The connection returned is a physical connection (a socket) which is adequate for a 2-tier client-server architecture as each client will create and use its own connection and seldom sharable.
JDBC v2.0 uses DataSource to support Java Transaction API and a 3-tier architecture. An intermediate layer (application server) sits between client and the database. DataSource returns a logical connection from a connection pool which improves performance by avoiding set up time for every JDBC connection request.
