The index information for the external storage system is separated from the data information by the SAP System and transferred to two files (data file and description file):

Data files contain the actual data information (print lists).

Description files contain the index information.

In the case of print lists, separation into data files and description files occurs in the spool system.

This means that when print lists are stored, the SAP application itself must write the index information to the print list. The index information is then extracted in the spool and stored in the description file.