Colour Books Of
COMPACT DISC

YELLOW BOOK

Yellow Book defines CD-ROM or Compact Disc-Read Only Memory was announced by Philips and Sony in 1983.

CD-ROM was envisioned as a way to allow digitized content including but not limited to audio to benefit from the capacity, durability, and economies of scale that were rapidly making compact disc audio a big success.

Yellow Book is the disc specification that gave birth to all the variations on a CD theme that make CD formats so versatile and, equally, so confusing.

At its lowest level, Yellow Book specification for CD-ROM is nearly identical to RedBook, in that it retains the TOC, Lead In, Program area, Lead Out, and basic error correction.

But the next level of Yellow Book organizes the frames defined in Red Book into sectors (98 frames, or 2,352 bytes, equalsone sector) and adds another layer of error detection and correction.

The extra error correction information, at 288 bytes per sector, plus 12 bytes of sync and 4 bytes of header, reduces the available sector space for user data to 2,048 bytes. Addresses of sectors are expressed as minutes, seconds, and sectors (MM:SS:SS).

Yellow Book stops there, however, leaving it up to the CD-ROM developer to decide how to arrange sectors into logical blocks and logical blocks into files. And that is the first step into the complexity of CD, in the form of Mode 1 and Mode 2.

The Yellow Book specification defines two data structures: Mode 1 and Mode 2. The mode byte, which is included in the header field of a CD-ROM sector, describes the type of data contained in the data field.

Mode 1 denotes CD-ROM data with Error Correction Code (ECC), which provides room for 2,048 bytes of user data and is the mode used to store data that is unforgiving of error.

Mode 2 denotes a sector with data stored without ECC, which provides more room (2,336bytes) for user data, but which is typically used for data that is more tolerant of error. Mode 2 is a way of interleaving sectors of data with extra error correction (Form 1) with sectors of data without extra error correction (Form 2), since Mode 1 does not allow unlike sectors to reside in the same session on a disc. The Mode 2 branch of the family tree is the show-biz side.

In the early days of CD-ROM publishing, each developer used a different, incompatible file format for CD-ROM. This problem was addressed by the High Sierra Group, an ad hoc committee of CD-ROM developers who created the High Sierra Format, which was later adopted, with minor revisions, as ISO 9660, the logical file format for CD-ROM.

There are three Levels of Interchange within ISO 9660:

• Level 1 requires that each file be recorded as a continuous stream of bytes, with filename conventions that are similar to the restrictions of DOS
• Level 2 relaxes the filenaming conventions, among other things
• Level 3 is total freedom.

ISO 9660 was what gave rise to the claim "any disc plays in any drive" for CD-ROM.

Unfortunately, the lowest common denominator approach in ISO9660--Level 1--was not optimal for operating systems other than DOS. Apple's long filenames and data and resource forks, and UNIX's deep directory structures did not fit well into the ISO 9660 Yellow Book mold. But even as the seemingly rigid Red Book could be adapted to do what it was never designed to do, so could ISO 9660 be adapted to suit the purpose.