Why driver does not need to be registered?

Hi

I'm using postgresql-8.3-604.jdbc3.jar driver

I have a very simple java program to inspect what drivers are initially
loaded:

import java.sql.DriverManager;

public class TestDrivers {

public static void main(String [] argv) {

java.util.Enumeration myDrivers = DriverManager.getDrivers();

while (misDrivers.hasMoreElements()){
System.out.println(misDrivers.nextElement());
}

}

}