Both and studio and runtime provide all of the JDBC drivers for the supported databases with the one exception being MySQL. For MySQL you will need to download the driver Jar file from the MySQL site and put it in the directory identified by the studio which is shown when you attempt a Test Connection in the database properties. You will need to do this only once for your installation of Data Mapper. You will also need to include this Jar file in your runtime classpath.
Custom database drivers are also possible (see below), and they require the using the project classpath mechanism and including the Jar file in the runtime classpath.