UDF

Universal Disc Format
A CD File System standard.

UDF allows for adding files and folders, and that's why it is used by Packet Writing Software.

This File System is mandatory on DVDs but also allowed on CDs.
It is known by Win98 if 1.02, known by Win2K if <= 1.5, known by WinXP if <= 2.01 (in case the CD / DVD session is closed).