select col_1, col_2, rowid from some_table
A rowid identifies a row in a table
A rowid is a pseudo column (like versions_xid), that uniquely identifies a row within a table, but not within a database. It is possible for two rows of two different tables stored in the same cluster to have the same rowid.
In order to find the datafile, block number and slot number, dbms_rowid can be used: