The minimalism that helped make the ISO 9660 standard successful may sometimes be too minimal for specific applications (such as distributing POSIX based, bootable CD-ROMs). Because ISO 9660 does not adequately support the POSIX file system, the Rock Ridge Group was formed to develop ISO 9660: 1988 extensions, which take advantage of the system-use area of the directory record (provided for in ISO 9660) to store complete POSIX file system information.
Extensions to ISO 9660 can make a CD-ROM appear like a given target operating system (such as a POSIX compliant file system).
By encoding these extensions (using the sharing-use protocols), you can allow for separate sets of attributes for the same file system.
This lets you organize extended information for different systems (such as VMS, DOS, and UNIX) in a nonconflicting way. Also, any system that only understands ISO 9660 without any extensions can still gain access to the files and obtain the exact same contents of data for a file.
If the extensions are not understood, they are not used at all. You get the best of both worlds: ISO compatibility and interoperability, and POSIX operating system transparency and functionality.
Technology is not standing still also, because Philips and Sony just proposed a new CD-ROM standard which could contains 2.3 Gbytes of data (almost 4 times more than current CD-ROM standard). Probably the current ISO 9660 standard has to be adpated too with new extension attributes for new applications (to be defined).