TOC - directory or folder

from the CD-Recordable FAQ, by (fadden@fadden.com)
2-27 What's a TOC? How does it differ from a directory?

The TOC (Table Of Contents) identifies the start position and length of the tracks on a disc. The TOC is present on all CDs. If it weren't, the disc would be unreadable on a CD player or CD-ROM drive. CD recorders write the TOC as part of "finalizing the disc. (Section (2-19) has some more details  about finalizing discs.)
A "directory" is a list of files. If you're a Mac user, you're probably used to the term "folder". It's part of a filesystem, such as the ISO-9660 or HFS filesystem present on most CD-ROMs. Audio tracks don't have files, so they don't have directories either.
There's nothing stopping you from writing a FAT16 or Linux ext2 filesystem directly onto a CD-ROM. Whether or not you can read such a disc is a different matter. (The Linux "mount" command should allow you to mount just about anything read-only, but Windows may not be so willing.) The CD specification defines the TOC, and there are well-defined standards for certain filesystems, but [AFAIK] nothing in the CD spec requires that you fill a data track with a certain kind of data.

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