What Is a Multi-Session CD?

Some optical discs were recorded in multiple sessions. Depending on the software and drive, later or earlier sessions may not be immediately visible.

What is a session?

Multi-session discs can contain more than one recorded session, and the visible directory may not represent everything recorded on the medium.

Why files may appear missing

Identify the session structure before extraction and avoid assuming that the first mounted filesystem is the complete source.

Recovering earlier sessions

Where recovery requires specialist optical-disc tools, preserve the original session information and create a documented image or extraction.

Disc imaging

Recovered files should be associated with the session from which they originated.

Verification

Record session count, file counts, checksums and any inaccessible sessions.

Reference guidance: This article is informed by optical-media preservation guidance from the U.S. National Archives and the Library of Congress Recommended Formats Statement. Where appropriate, the article distinguishes preservation guidance from practical extraction procedures.