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Purple Craze: Sony Opens Book on Double-Density CD

by Dana J. Parker

This month, dear readers, let's jump into the Wayback machine and set the dial to 1993. That was the year, if you recall, that the demand for higher density CDs began, and it was inaugurated when Nimbus Technology and Engineering, of Gwent, Wales, demonstrated a double-density Red Book (CD-Audio) disc containing two hours of MPEG-1 video at the Midem show in Cannes in January. Nimbus chose the Red Book platform because at the time there was no other choice. Philips had yet to announce the Video CD standard or to deliver the FMV cartridge for full-motion video on CD-i players, and CD-ROM, with its high overhead of error correction and detection, limited the capacity and playback speed of video data. In October of that year, Optical Disc Corporation demonstrated a double-density, White Book format Video CD played back on a Video CD player at the SMPTE (Society of Motion Picture Technicians and Engineers) show.

being dense

Traditional standards-setters Philips and Sony found themselves in an embarrassing position: the ability of higher-density compact discs to contain and play back two hours of video on existing platforms had been demonstrated, yet there were no announced plans for an official Philips/Sony pedigreed, high-density disc format. Philips and Sony objected to the illicit violation of the Red Book and White Book specs on the grounds of incompatibility. This may have been what led to Philips' announcing, in early 1994, that the waiting world could expect a high-density standard that would hold up to four times as much data as existing discs, including video. By December of that year, Philips and Sony had announced MMCD. In January 1995, Toshiba and Time Warner announced what they called SD, for Super Density disc. After months of bickering and positioning (some of which is still going on), we ended up with DVD.

Fast forward to the present day, and what do we have? Just when you thought it was safe to assume that the final chapter in the colored CD books had long since been written, out comes a whole new volume to complete the spectrum of standards: Purple Book, or (tentatively) Double Density CD (DDCD). And as it turns out, it looks eerily similar to the very same double-density formats Philips and Sony rejected back in 1993.

For starters, the media will indeed be double density, at 1.3GB. The form factor remains the same, as does the laser wavelength (780nm) required to read the media. And just like its unapproved predecessors, it will not be readable in existing CD-ROM drives and CD-Audio players. Track pitch has been tightened to 1.1 micrometers, minimum pit length reduced to 0.623 micrometers, and scanning velocity slowed to 0.9 meters per second. According to Sony, disc manufacturers won't be required to upgrade their existing replication lines to make the new DDCD media, but it's not clear, as yet, if changes will be required in the process of creating glass masters.

But there are differences, as well, between the old and the new; while it's possible to make DDCD read-only discs, the format will debut in recordable and rewritable media. Sony has no plans to manufacture read-only drives that can handle the media, but will create DDCD-R/RW drives that can read any flavor of CD, record CD-R, rewrite CD-RW, and read, record, and rewrite DDCD. The format also specifies new error correction called CIRC7, a beefed-up version of the ISO 9660 file format, and a slightly larger numeric aperture. These changes will require a new logic chip, recently made available for licensing by Cirrus Logic, and new recording/rewriting software, reportedly being developed by Prassi.

cool, but what's it for?

Good question. Sony and Philips see this as a "natural migration path," a "low-cost solution to high-capacity discs that inherit the basic specifications of the CD formats." For now, recorders are planned only for the desktop market, not for integration into consumer-integrated PCs. However, let's not rule out the possibility of a DDCD-RW-based version of the cool new Sony Mavica CD1000, the digital camera that records to 8cm CD-R media-that is, if the desktop drives take off. With DDCD, you can back up your hard drive if it's smaller than 1.3GB or if it's worth it to you to cut the number of CD-R/RW discs you're currently using to back up in half. The format, like CD-R/RW, is content-neutral, so there's no reason you can't use it to store MP3s, Video CD, DVD-Video, JPEGs, MPEGs, or Aunt Edna's coleslaw recipe.

And just coincidentally, of course, the cynic in me can't help but note that it's a way to extend the life and expand the applications of writable CD. In case you hadn't noticed, the alternatives-the DVD writable formats-are still in a state of appalling disarray and confusion. So, you say you need more recordable and rewritable storage area, but can't afford a DVD-R, can't wait for DVD-RW, or can't decide between DVD-RAM and (soon to come) DVD+RW? Well, here ya go: DDCD.

Purple Book was due to be finalized by Philips and Sony in September 2000. By the time you read this, it may already have been announced. Whether it will fly or not is anybody's guess.


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