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

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

Where can I find the new 90 minute CD-R discs? Why were they previously unavailable?

Hurry and jump from the 80 minute frying pan into the 90 minute fire. The maximum capacity of a disc that fully conforms to the Philips/Sony Orange Book standard is 74 minutes. Higher capacities require a forgiving write or read drive. Some drives tolerate defects but many do not.

Program area diameters must be between 50 mm and 116 mm. Successful optical resolution of data requires a track pitch of 1.6±0.1 micrometers and a scanning (constant linear) velocity between 1.2 m/s and 1.4 m/s at 1X.

74 minute discs normally use a track pitch of about 1.59 micrometers and a scanning velocity close to 1.22 m/s. Adequate margins absorb normal manufacturing variations. Higher 80 minute capacities are achieved by reducing track pitch to 1.497 micrometers and by lowering the scanning velocity to 1.1975 m/s. Not only are these values outside specified limits, manufacturing process variations make the situation even worse. The result is unpredictable write and read quality.

90 minute discs have nominal track pitch and scanning velocity values that are significantly outside specified limits. Such discs also violate addressing requirements of the standards that allow a maximum ATime in the program area of 79:59:74, or 80 minutes.

Of course, rules can be broken sometimes without suffering the consequences of such actions; but not always. Because there are no drive standards, discs that work in some drives can fail in others. If the disc conforms to media standards, then the drive is at fault when failure occurs. If the disc violates media standards, then the disc is at fault when it cannot be written or read.

Increasing volume and falling prices for both media and drives often result in quality problems. Even 74 minute discs can fail interchange and longevity requirements. Pushing the envelope with 90 minute, or even 80 minute discs, is a sure path to failure.

Reliable, 63 minute CD-R and CD-ROM discs were once common. Performance of such media was very reliable for several reasons, including a conservative design that stayed well within program diameter, track pitch, and scanning velocity limits. Such discs are rare today because of the popular demand for higher and higher capacities.

74 minute CD-R discs represent the highest capacities that can achieve dependable interchange. If you bend or break the rules then be prepared to accept the consequences.