postmaster & JDBC

Hi -
I'm a little confused at how the JDBC driver and the postmaster get along.
I have a servlet system built that uses connection pooling to create a
number of Connection objects to a PostgreSQL (6.5) database.   I start out
by creating 5 connections and up that by 3 new ones if it runs out of
connections (which hasn't been an issue yet).  Anyway, I just read the man
page for postmaster this evening and noticed this comment:
*****      Only one postmaster should be running at a time in a given Postgres
installation."  Here, an  installation  means  a database directory and
postmaster port number.  You can run more than one postmaster on a machine
only if each one has a separate directory and port number.

*******

As I haven't been doing either of the aforementioned things (separate
directory and port number for each postmaster), is the JDBC driver doing
this for me?  It seems that they must be all running on the same port
because I'm calling a DriverManager.getConnection() with the same URL.

Thanks for any explanation into how this works.

Mike