Jolitz Heritage

Extending Standards for CD-ROM

Extending Standards for CD-ROM 6/93 Dr. Dobbs Journal, USA: Extending Standards for CD-ROM, Lynne Greer Jolitz . Although ISO-compliant CD-ROMs are interchangeable and usable on any type of system, the minimalism that made the ISO-9660 standard successful is sometimes too minimal. Consequently, the Rock Ridge Group and others have developed extensions to give new life to CD-ROMs. "Most programmers are aware of the ISO-9660 standard and its significance in sharing CD-ROM data between different platforms. In our article "Inside the ISO-9660 Filesystem Format" (DDJ, December 1992), we examined how this standard has encouraged the use of CD-ROM technology and how a modern ISO-9660 CD-ROM is structured. ISO-compliant CD-ROMs are interchangeable and can be used on any type of system and architecture. However, 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 filesystem, 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 filesystem information. Extensions to ISO-9660 can make a CD-ROM appear like a given target operating system (such as a POSIX-compliant filesystem). By encoding these extensions (using the sharing-use protocols), you can allow for separate sets of attributes for the same filesystem. 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; you aren't precluding any use of CD-ROM by the use of extensions, you're simply extending the scope of use of the information. " [To continue reading this article, simply click here to register or login at DDJ.]