To Everything There Is a Session: A Time to Listen, a Time to Read Multi-session CDs

When the cost of CD burners dropped precipitously in the late 1990s, consumers had access to the CD-R, a format with far greater storage capacity than floppy disks. Multiple session standards allowed users the flexibility to add subsequent content to an already-burned CD-R, which made them an attractive option for personal backups. In a digital preservation context, CDs with multiple sessions can pose significant challenges to workflows and can lead to data errantly not being acquired or reviewed if users are using a workflow designed for single-session, single-track CDs. In workflows that include CDs as software installation or transmission media, extra-session behavior can have an impact on software supply chain review. 

This article provides an overview of the structure of a multi-session CD and outlines tool behavior of disk images generated from multi-session CDs. To support testing in specific contexts, we provide a guide to creating a multi-session CD that can be used when developing workflows. Finally, we provide techniques for extracting content from physical media as well as existing disk images generated from multi-session CDs.