An extended rowid has a four-piece format, OOOOOOFFFBBBBBBRRR:

OOOOOO: The data object number that identifies the database segment (AAAAao in the example). Schema objects in the same segment, such as a cluster of tables, have the same data object number.
FFF: The tablespace-relative datafile number of the datafile that contains the row (file AAT in the example).
BBBBBB: The data block that contains the row (block AAABrX in the example). Block numbers are relative to their datafile, not tablespace. Therefore, two rows with identical block numbers could reside in two different datafiles of the same tablespace.
RRR: The row in the block.
SELECT ROWID,
SUBSTR(ROWID,1,6) "OBJECT",
SUBSTR(ROWID,7,3) "FIL",
SUBSTR(ROWID,10,6) "BLOCK",
SUBSTR(ROWID,16,3) "ROW"
FROM products;

ROWID OBJECT FIL BLOCK ROW
------------------ ------ --- ------ ----
AAAA8mAALAAAAQkAAA AAAA8m AAL AAAAQk AAA
AAAA8mAALAAAAQkAAF AAAA8m AAL AAAAQk AAF
AAAA8mAALAAAAQkAAI AAAA8m AAL AAAAQk AAI

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rowID explaination