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DVD Tracks and Sectors

Data Encoding on a CD

DVD Formats and Standards

Compact Disc information and CD Drive Formats

CD ROM File Systems

Installing and Configuring an ATAPI Tape Drive

Installing and Configuring a SCSI Tape Drive

A Brief History of CD

DVD History

Configuring Windows 9X/2000/XP to Support a Tape Drive

CD ROM and CD R tracks and sectors

Manufacturing process for data CD ROM and audio CD

Things to consider when working with FDDs

Optical media sing a siren's song with their high storage densities. They captivate engineers with the dream of building a better hard disk, a device that can read and write like a hard disk but with the storage densities only achievable through optical means. Compact Disc-Erasable, or CD-E, is the pot of gold at the end of the rainbow of their dreams.

CD-E is actually the third incarnation of phase-change technology. The first drives, under the Phase Change Recordable banner or PCR, were made by Toray Industries. They used a medium slightly larger than CDs, 130 millimeters in diameter as opposed to the CD's 120 mm, and were consequently physically incompatible with CD drives. Both sides of the disc had a recordable surface, allowing for a total capacity of 1.5GB per disc. Panasonic's PD discs reduced the size of the disc to the same as CDs and modified the storage format. The actual writing format uses sectors of 512 bytes versus the 2048-byte or larger sectors used by CD, so PD disc are also logically incompatible with CDs. You cannot duplicates a CD on the PD medium. Moreover, the logical format of the PD system limits its capacity to 650MB per disc as opposed to the 680MB total of CDs. Further, the phase-change material used by the Panasonic PD drives is not compatible with the optical heads and electronics of CD drives. Although the electronics of the Panasonic drives adapted to handle either phase-change or conventional CD media, PD discs work only in PD drives.

CD-E media use a reformulated optical compound that more closely-but not perfectly-matches the response of conventional CD media. For CD-E discs to be compatible with CD drives, the drives need a slight modification in their electronics to compensate for the lower reflectivity of the CD-E phase-change media. Conventional CDs reflect 70 percent of the laser light striking them; CD-R discs reflect about 65 percent; the CD-E media reflects only 15 to 20 percent of incident light. The necessary circuitry is called automatic gain control, and is incorporated into many new CD drives. To be compatible with conventional CD players, the discs made with a CD-E drive must conform to the ISO 9660 format.

In operation, a CD-E drive is more like a conventional hard disk than a CD-R. The drive can update the disc table of contents at any time so you can add files and tracks without additional session overhead. Because of the limited life cycle of the phase-change medium, however, the CD-E format works best with operating system modifications similar to those used by Flash memory drives that minimize directory updating that may wear out the media prematurely.

Despite its ease of use and flexibility, most optical manufacturers don't believe that CD-E will replace write-once CD-R, at least in the near future, because of media costs. Phase-change media are more expensive to produce than simple stamped CD-R discs. Currently the difference is more than a factor of five.