//host:port/service_name connection string format

Hello,
I am trying to figure out which version of Oracle (version, meaning not only 9 or 10, but down at least to the minor, e.g. 9.0.2.0), requires the following connection string format:

jdbc:oracle:thin:@//host:port/service_name

and from which versions is the "//" part only optional (so jdbc:oracle:thin:@host:port/service_name is allowed)?

Thanks!