Data CD is the most frequently used format disc. Its Optical tracks have the following features: It has only one session, one Optical track; it can be used in many sessions and many Optical tracks. The CD has a directory structure.
The above picture is the Optical track structure of KILL98 software disc. From the picture, we can see the disc has one session; this session has only one Optical track set with directory structure that tally with ISO9660 standard. The software CDs published by software developers all have only one session and one Optical track. The computer fans, they would like to adopt multi-tracks and sessions while burning CDs. As the sessions would keep a 13 MB as intervals between each other, there would be a waste of space on CD-R. So it is not suitable for multi-session burning.