One reason for the hybrid format is the restrictions of ISO 9660 (filenames of only eight characters, and a maximum depths of eight directories, similar to the Microsoft FAT file system). Another key factor is that ISO 9660 does not support resource forks, which is critical to the classic Mac OS' software design (OS X or macOS removed much of the need for resource forks in application design). Companies that released products for both DOS (later Windows) and the classic Mac OS (later macOS) could release a CD containing software for both, natively readable on either system.