Hybrid CD

Multiple file systems

A hybrid disc is an optical disc that has multiple file systems installed on it, typically ISO 9660 and HFS+ (or HFS on older discs). One reason for the hybrid format is the restrictions of ISO 9660 (filenames of only eight characters, and a maximum depth of eight directories, similar to the MicrosoftFAT file system). Another key factor is that ISO 9660 does not support resource forks, which is critical to the classic Mac OS software design. Companies that released products for both MS-DOS and Classic Mac OS could release a CD containing software for both, natively readable on either system. Data files can even be shared by both partitions, while keeping the platform specific data separate. In a "true" (or "shared") hybrid HFS filesystem, files common to both the ISO 9660 and HFS partitions are stored only once, with the ISO 9660 partition pointing to file content in the HFS area (or vice versa). Blizzard Entertainment has released most of their computer games on hybrid CDs. By default, Mac OS 9 and OS X burn hybrid discs.