The Evolution and Standardization of CD-ROM

The Evolution and Standardization of CD-ROM[1]

As briefly discussed earlier in Chapter II, Section 1.3 of this document, CD-ROM represents the application of the widely accepted CD Audio technology to the storage of digital data for computers. CD Audio owes much of its success to the fact that two industry leaders, Phillips and Sony, settled early on a standard for the placement of audio on a compact disc, and published it in what has become known as the “Red Book” in 1980. Industry acceptance of that standard was quickly accomplished, and the stage was set for the release in 1983 of a second publication, the “Yellow Book”, specifying certain standards for CD-ROM. The Yellow Book deals chiefly with the division of the disc into sectors, where data will reside, and defines how those sectors are individually labeled and addressed. It also defines how the data space within each sector will be divided into an information-containing region and an error-correcting region. The effect of these standards is to raise the reliability of the CD Audio disc to a point where it becomes acceptable as a computer storage medium; with error correction implemented, on the average only 1 in every 20,000 CD-ROM discs will contain an unrecoverable data error.

Although the Yellow Book quite adequately specified the physical format of the CD-ROM disc, it did not attempt to address the way in which sectors on the disc would be grouped into files, and how those files would be named and located. It quickly became apparent to the many vendors adopting the Yellow Book standards that it would be to their advantage to adopt such a standard for files; in this way, a file of information could be placed onto a disc by any vendor with the assurance that another vendor’s software would be able to locate and read that information. Fourteen vendors first met in September, 1985, forming what came to be known as the High Sierra Group. A series of monthly meetings was quickly successful in developing a proposed standard known as the High Sierra Proposal, which was submitted to international standards groups for consideration in June 1986. Although final approval of that proposal is not expected until 1988 or 1989, acceptance is widely viewed as certain, since no competing standards have been put forward. In the meantime, vendors have proceeded with their development of CD-ROM discs and file system software, treating the High Sierra Proposal as a de facto standard.

It is important to note that the High Sierra Proposal only specifies the format of directories on a CD-ROM disc, and how they point to files; it does not specify the format or structure of data within a file. This allows vendors the freedom to select file formats most appropriate to their applications, allowing sequential files, indexed files, or more sophisticated database formats. In addition, the High Sierra Proposal allows a file to span multiple discs, so that the maximum size of a CD-ROM file is not limited to the size of a single CD-ROM disc. Systems hosting multiple CD-ROM drives would thus be able to access any record on a multi-disc file, without the application program having to know which CD-ROM drive was being accessed. Importantly, the low cost of CD-ROM drives makes it feasible to support such applications, and the widely adopted SCSI interface method allows multiple drives to be conveniently supported by a single controller.