Frequently Asked Questions About CD-R and CD-RW Discs

Please contact Media Sciences if your questions are not answered on these pages.

Why do I hear so much about CD-R problems? Isn't CD-R the same as CD-ROM, a trouble-free product?

First of all, CD-ROM is not trouble-free. Known CD-ROM manufacturing and handling techniques exist that can produce high quality discs, but not everyone follows them. CD-R technology is not as mature, and procedures that will generate high quality one offs are not always used.

CD-R technology is still evolving, as evidenced by the lack of a public ISO standard. The proprietary Orange Book Part II specifies format, physical, mechanical, dimensional, and optical specifications. It does not specify the method required to manufacture CD-R discs, and the industry is split between stabilized cyanine and phthalocyanine dyes. Each requires different laser beam powers and write strategies for optimum results. Since a standard for writers does not exist, model "A" might work well with certain brands and poorly with others. Results from model "B" might be opposite to those of "A". Throughput requirements complicate matters as higher speed writers become popular.

Different recording methods can cause problems. Single session CD-R discs are recorded with one lead-in followed by an information track, then lead-out. Such discs are readable by most CD-ROM drives conforming to Yellow Book standards. Multi-session CD-R discs contain multiple information tracks, each preceded by lead-in and followed by lead-out. Disk-at-once recording writes the entire disc in one pass. This disc can be read by drives conforming to Orange Book Part II, while other players should at least be able to read the first track.

Historically, multi-session recording has been track-at-once. Tracks are recorded intermittently, and a record of their location is maintained in the Program Memory Area. Finalization is the last step when the record is transferred from the Program Memory Area to the conventional Table of Contents. Corrupted data can be left in the "write splice" pre-gap area following the lead-in with Table of Contents and preceding track one. Many CD-ROM drives will ignore such an area, but some will be adversely affected. Again, standards for drives do not exist.

Several steps exist that can lead to high quality CD-R one offs. First, sort out the Red Book/Yellow Book/Orange Book/Green Book/White Book/Blue Book/Photo CD issues. Select those required for compatibility, and verify that your users will have players that meet the required standards. Second, select the appropriate recording method. Be sure to verify that all of your users have multisession playback capability if that method is used. Third, do-it-yourself production may not be best, even if you have diskette duplication experience. Use a high quality service agency to quickly ramp-up production and enhance quality. If you decide on an in-house capability, try not to build your recording area one piece at a time. Buy a system, not parts. Obtain the software, writer, and discs as a package having proven performance.

The final step to achieving CD-R quality is testing. Bad discs are often detected only by the end user, since read-after-write can only verify the presence of the proper data. More sophisticated tests are required to assure interchange in all drives. Test data can provide confidence that a new system is functioning properly, and can furnish evidence of continuing performance. A comprehensive test menu will result in a high level of confidence, while a proper sampling plan can result in low cost. CD-R quality management involves more issues than does CD-ROM, but all the tools exist. Use them.