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.
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
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