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The DVD Writer: Just Scratching the Surface--Writable Optical Disc Protection
Posted Aug 16, 2005 Print Version     Page 1of 1
  

Let's face it--writable CDs and DVDs are tough but they can be damaged. Scratches, scrapes, fingerprints, dust, and just plain crud can play havoc with reading and, especially, with writing. Dealing with these everyday realities in ways that keep discs realistically priced and marketable remains a challenge for product designers.

Efforts to improve CD-R and CD-RW media durability largely focus on applying a protective topcoat (pioneered by Kodak as part of its original InfoGuard system) to the disc's conventional lacquer overcoat. Since the information-bearing layer rests just below the disc's label surface, the topcoat helps shield data from physical damage. However, this approach does nothing to reduce injury to the laser incident (read/write) side of the disc or assist writable DVDs and next-generation HD DVDs and Blu-ray Discs (BD).

To provide such protection, and to keep discs free of fingerprints, dust, and the like, enclosed caddies were used in many early CD-ROM drives and recorders. Some DVD-RAM configurations still employ cartridges and even forthcoming BD-R/RE and HD DVD-R/RW allow for this option. Marketers universally revile caddies and cartridges as clumsy and expensive solutions designed by engineers. Thus, manufacturers rely upon on a variety of recorder technologies and media design elements to manage the effect of disc surface aberrations. Mainly, adaptive laser power control (such as ROPC and WOPC), increased recording layer sensitivity, defect management, enhanced error detection and correction, improved servo stability, and the intrinsic optical protection of the substrate (CD/DVD/HD DVD) or cover layer (BD).

FUD (fear, uncertainty, and doubt) is a powerful selling tool, especially when it comes to preserving personal memories, and technology. And user cleaning can compensate for only so much. Thus, most major disc brands are rolling out premium hard coated writable CDs and DVDs. Hard coating is also said to be key to the viability of upcoming BDs. Catchy names abound including Imation's ForceField, Verbatim's VideoGard/ScratchGuard, TDK's Durabis, Maxell's MaxPro Hardcoat, Memorex's DuraLayer, Panasonic's Pro Hard Coating, Prodisc's Hard Coat, and Sony's AccuCORE.

A hard coat provides one or several additional layers of durable thin film engineered to resist scratches and smears, repel dust, and sometimes protect against UV. The first widescale use of hard coating in optical storage came in the production of magneto-optical (MO) discs. Applied using spin coating and vacuum deposition, a variety of materials were employed including silxoane and UV curable resins and metal oxides such as ITO, silicon dioxide, and tin oxide. Hard coats for current and future optical discs build on this foundation with new materials and process, such as lamination, in current use or under development.

Impressive? You bet! But hard coating is not a magic bullet. Components can be expensive, require additional production steps (each with their own yields) and some of these materials are brittle. Also, I have yet to hear of any independent accelerated age testing to suggest how treated CDs and DVDs might hold up over time.

An unorthodox design from a recent upstart promises alternative protection. In addition to a hard coat, the SLDI Scratch-Less Disc incorporates bumps on a CD or DVD substrate (in non-data bearing areas) to act as pedestals to raise a disc above any flat surface on which it is placed. This is said to protect a disc from scratches or gouges when stacked or dragged over a desktop. Its developer assures 99% compatibility with existing drives but I have yet to encounter any supporting data or assessments of possible side effects.

I welcome anything within reason that improves writable disc durability and system robustness. But even clever designs, ingenuous technologies, and advanced materials have their limits. My best advice remains to always follow manufacturer recommendations and encourage careful handling and storing of all optical media.

Hugh Bennett (hugh_bennett@compuserve.com), an EMedia contributing editor, is president of Forget Me Not Information Systems (www.forgetmenot.on.ca), a reseller, systems integrator and industry consultant based in London, Ontario, Canada. Hugh is the author of Understanding Recordable & Rewritable DVD and Understanding CD-R & CD-RW, both published by the Optical Storage Technology Association (OSTA).

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