Suppose that on one server you have three databases in three separate home directories: Oracle7 (7.3.3), Oracle8 (8.0.6), and Oracle8i (8.1.6).

In this configuration you can have an Oracle7 client connected to the Oracle7 database. Another Oracle7 client can connect to the release 8.0.6 and 8.1.6 databases.

In addition, a release 8.0 client is connected to the Oracle7 and release 8.0.6 databases, and another release 8.0 client is connected to 8.1.6.

Finally, a release 8.1 client is connected to the Oracle 8.1.6 database.