Page "ISO 9660" Paragraph 39

The restrictions on filename length ( 8 characters plus 3 character extension for level 1 ) and directory depth ( 8 levels, including the root directory ) are a more serious limitation of the ISO 9660 file system.

Many CD authoring applications attempt to get around the filename length by truncating filenames automatically, but do so at the risk of breaking applications that rely on a specific file structure.