The file directory is an internal administration structure of the database system. The file directory contains the following, among other things:
Assignment of the root pages of the B* trees to the table IDs
Assignment of the initial pages of page chains to the table IDs
Type flags (specify whether a table contains primary data, secondary keys or LOB values)
Statistical information on the number of data records and the size of the tables
Each internal file in the file directory has a unique file number (8 bytes long).