The most famous limitation of Oracle 10g XE was the . The database could store up to 4GB of user data. This excluded system data, temporary space, and undo segments. For a student or a small departmental application, 4GB was massive. However, once the database hit that 4GB ceiling, it would stop accepting new data. (Later versions, like 11g XE, increased this to 11GB).
To avoid conflicts with existing Oracle instances on a developer's machine, XE defaulted to non-standard ports: oracle database express edition 10g