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Eastman Kodak Proposes New Hard Sector CD-DASD Format for Removable, Rewritable Storage

Developed by Kodak engineers in conjunction with Dennis Howe of the University of Arizona Optical Data Storage Center, the Compact Disc—Direct Access Storage Disc (CD-DASD) format is positioned by Kodak as the next logical and necessary step in the evolution of CD-Recordable and CD-Erasable (CD-E) technology.


Eastman Kodak Proposes New Hard Sector CD-DASD Format for Removable, Rewritable Storage

Hugh Bennett
CD-ROM Professional, April 1996

At the February 6, 1996 meeting of the Optical Storage Technology Association (OSTA) in San Francisco, Eastman Kodak presented a proposal for a new CD recording format using individually addressable hard sectors similar to those used by other rewritable storage technologies like magneto-optical and phase-change. Developed by Kodak engineers in conjunction with Dennis Howe of the University of Arizona Optical Data Storage Center, the Compact Disc—Direct Access Storage Disc (CD-DASD) format is positioned by Kodak as the next logical and necessary step in the evolution of CD-Recordable and CD-Erasable (CD-E) technology.

Philip Ashe, Director of Strategic Planning for Storage Products at Kodak, says the purpose of CD-DASD is to merge the best elements of CD-R, CD-E, and rewritable devices in a single product that combines CD writers and readers with CD-DASD capabilities to provide users with a single interchangeable, high-performance, and high-capacity storage solution at low media costs.

Membership Has Its Privileges
According to Kodak’s proposal, there are significant benefits to adopting their new format. The most obvious is that it makes operating the device more user-friendly. From within applications, users could simply read, create, and save updates to a CD-DASD device directly from a PC or across a network just like a hard drive. If files need to be shared, existing CD-Recordable software and writable discs could be used.

The proposed format would use a pre-sectored erasable or write-once disc, or—much like formatting a floppy diskette—today’s CD-R discs could also be used by drives creating a soft-sectored CD-DASD format. This involves writing sector headers synchronized with their ATIP (Absolute Time In Pregroove) channel and generating a defective-sector table.

By eliminating the possibility of buffer underrun, the new standard would allow users to write as little as 4KB of data at a time with no need for the run-in/out and link blocks that take up valuable space on packet-written discs. CD-DASD also holds the promise of increased performance with immediate read and write access to discs similar to that delivered by magneto-optical devices, according to the Kodak proposal.

Details, Details
The Mode 1 sector type currently in use with CD-ROM is based on 98 Eight-to-Fourteen-Modulation (EFM) frames holding 2,048 bytes of data. The CD-DASD format employs two logical sector types utilizing 196 EFM frames with either 4,096 byte (Mode 01) or 4,506 byte (Mode 02) user data sizes.

CD-DASD maintains low and high-level compatibility with current CD formats by retaining such items as the subcode channel, EFM, and ATIP signals. It also uses C1/C2 Cross Interleaved Reed Solomon (CIRC) Error Correction Codes (ECC) as the basis for a “disc-level ECC” system with reliability described by Kodak “at least as good as that provided by CIRC.” Mode 01 CD-DASD sectors provide an extra layer of error detection and correction for higher data reliability. Even the overhead using Mode 01 sector sizes is identical to current CD-ROM, packing 650MB of data into a 74-minute disc.

Due to its similarities to existing CD-ROM formats, hardware manufacturers must make only a few modifications to their devices to take advantage of CD-DASD. In addition to more firmware programming, writers and readers must add encoder/decoder logic gates and controller logic.

Universal Removable Storage
The hope underlying the CD-DASD proposal is the possibility that CD-R and CD-E drives capable of reading and writing CD-DASD media as well as standard Compact Disc formats may serve as the sole removable medium storage device installed in computers.

Arizona’s Howe and Kodak’s Ashe believe such optimism is not unfounded because it is based upon the assumption that since almost every new computer sold includes a CD-ROM drive for reading commercial software titles anyway, a standardized read/write variant incorporating CD-DASD would be the most attractive as a floppy disk drive replacement. Ashe speaks confidently about market timing as a great “window of opportunity” with the growing industry acknowledgment that writable DVD derivatives will take at least several years to achieve significant market penetration.

The proposal also describes CD-DASD as being extensible to the next generation of technology and DVD computer peripherals. Howe promotes the value of using CD-DASD in conjunction with CD-Erasable as a way of gaining insight into some of the issues that will arise in the future with DVD-RAM.

Mixed Industry Reaction
Initial industry reaction to Kodak’s proposal seems mixed. Informal conversations with a number of CD-ROM drive and recorder manufacturers suggest that while CD-DASD is appealing, many in the industry are doubtful that it would be feasible to add support in their products.

The primary concern of the CD-DASD skeptics appears to be cost. According to Ashe, the approximate incremental manufacturing costs are $3 to $4 for writers, $2 to $3 for readers, and as low as $0.50 in DVD-ROM drives. He expects the cost increase would most likely be offset by the increased customer demand. Many characterize that as a “huge amount of money at the manufacturing stage” for any competitive high-volume environment. They point to the fact that their companies expect to ship at least 100 million CD-ROM drives worldwide over the next two years and millions of CD recorders, “so anything that adds cost to a drive is an extremely tough sell,” according to one in the doubters’ camp.

“Packet writing may have its rough spots, but we think it’s good enough for the general market,” one recorder manufacturer representative argues. “CD-DASD may be a superior answer, but the best solution isn’t always the most viable. It just looks like CD-DASD won’t add enough value for the average end-user to warrant the increased costs.”

Howe disagrees, pointing to the many limitations of packet writing and the fact that “computers will always need a removable storage device with higher DASD-like performance. If seen from an overall system perspective,” Howe continues, “computer manufacturers would gladly pay a little more for a CD-R/E/DASD if they could save $50 or more by not needing a floppy or other rewritable drive.” Laptops and notebook users would be the first obvious beneficiaries, though there is question as to how soon floppy disk drives could realistically be phased out of desktop machines.

Kodak anticipates that developer’s kits with quick turn gate arrays should be available by August/September 1996, making chip sets possible by the end of 1996. Based on that, Ashe says he anticipates CD-DASD-capable systems could be “available by the first half of 1997.”

(For more information regarding CD-DASD, contact Philip R. Ashe, Director of Strategic Planning—Storage Products, Digital and Applied Imaging, Eastman Kodak Company, Rochester, NY 14652-3819; 716/588-0667; Fax 716/588-5056; Internet—ashe@kodak.com.)


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 © Online Inc. / Hugh Bennett

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