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Blu-ray Disc and the Meaning of Backwards Compatibility

Change is unsettling. But, like it or not, change is once again upon us—this time with the arrival of next generation Blu-ray Disc (BD). Naturally, consumers and even professionals are apprehensive about this new format but, even so, BD’s promoters are doing an embarrassingly poor job of understanding and answering concerns. For example, manufacturers and content publishers amazingly have yet to clearly and consistently articulate BD device compatibility with CDs and DVDs.


Blu-ray Disc and the Meaning of Backwards Compatibility

Hugh Bennett
EMedialive, January 10, 2006

Change is unsettling. But, like it or not, change is once again upon us—this time with the arrival of next generation Blu-ray Disc (BD). Naturally, consumers and even professionals are apprehensive about this new format but, even so, BD’s promoters are doing an embarrassingly poor job of understanding and answering concerns. For example, manufacturers and content publishers amazingly have yet to clearly and consistently articulate BD device compatibility with CDs and DVDs.

What focuses my attention on this issue is a flurry of press releases distributed last week at the Consumer Electronics Show (CES) in Las Vegas. Proudly, some proclaim “Blu-ray Disc players will be fully backward-compatible with current CD/DVD formats” and others “Blu-ray Disc playback products are expected to be backward-compatible with the current DVDs, allowing continued enjoyment of existing DVD collections.” Disappointingly, these statements are not as defining as they might at first appear but more reminiscent of the unforgivably slippery language used regarding DVD/CD compatibility when DVD was released ten years ago.

Now, as was the case then, backwards compatibility is not mandated by official specifications, so it’s going to be a matter of choice for each individual hardware manufacturer. Thus, all marketers can claim is that it is possible to design BD devices that can read and write existing CD and DVD formats. They’ve made few efforts to clarify technical distinctions within and among the various disc families, and explaining how costs and market forces inexorably drive compatibility decisions hasn’t seemed a priority.

Physical, application, and logical considerations are all part of the technological compatibility picture. On the physical level, CDs, DVDs, and BDs are distinctly different from one another. Supporting all of them in a single device is a considerable challenge. Each employs different-sized pits, lands, tracks, and substrate thicknesses. Each is composed of disparate materials and is written or read using lasers of various wavelengths through lenses of assorted numerical apertures. Each format’s optical response is also carefully tuned so discs are not panchromatic.

Thus achieving physical compatibility requires BD players, drives, and recorders to incorporate involved optical pickups employing multiple lasers (780nm for CD, 650nm for DVD, and 405nm for BD) and numerous other clever tricks. DVD-RAM’s oddball nature (not to mention optional cartridge) requires still further hardware modifications be made.

As such, expect an array of device permutations on the market. For example, set-top BD players that work with DVD±R/±RW but not CD-R/RW or DVD-RAM. Perhaps computer recorders that read/write DVD±R/RW but not CD-R/RW or DVD-RAM or set-tops that write DVD-R/RW/RAM but neither DVD+R/RW nor CD-R/RW. And there will even be some units that try to do them all.

Application and logical layers muddy these waters still further. Even if a device can physically read a disc, the hardware must be programmed to decode and interpret its contents. For example, while all BD units will most likely play standard DVD-Video (DVD-V) titles, can the same be said for discs of the DVD-Audio (DVD-A) or DVD Video Recording (DVD-VR) persuasions? What about Audio, Video, or Super Video (CD-DA, VCD, SVCD) CDs? MP3/WMA CDs and DVDs? And while I’m at it, will all BD units support DVD content protection systems including Content Protection for Recordable Media (CPRM) and the Video Content Protection System (VCPS)?

In fairness, the transition to any new storage format is traumatic and managing it a tremendous challenge. That said, the optical storage industry should not squander its opportunity to start fresh and clean up the messes they created in the CD and DVD formats. And universally launching entirely backward-compatible BD products would be a good start. At the very least, the industry should provide clear explanations of any limitations up front, and go on to use consistent marketing language to let everyone know what BD truly holds in store.

ABOUT THE AUTHOR
Hugh Bennett, editor-in-chief of Hugh’s News, is president of Forget Me Not Information Systems, a reseller, systems integrator and industry consultant based in London, Ontario, Canada. Hugh is author of The Authoritative Blu-ray Disc (BD) FAQ and The Authoritative HD DVD FAQ, available on Hugh’s News, as well as Understanding Recordable & Rewritable DVD and Understanding CD-R & CD-RW, published by the Optical Storage Technology Association (OSTA).

Copyright © Information Today / Hugh Bennett

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