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HP Rewrites DVD Technology

How Labs Team Invented the First Rewritable DVDs Compatible With Standard Players

February 2002

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Imagine you're in the cockpit of a jet flying at 500 mph with a laser gun in your hand. Your target is a single cell on a single strand of hair. Your job is to hit that cell while zooming past at 500 mph. Now do it again.

That was, in essence, the problem that a team of HP Labs researchers studying peripheral storage systems set out to solve in 1996. The result of their efforts? The first rewritable DVD system (DVD+RW) compatible with standard DVD players.

photo: hp dvd+rw

The technology (introduced in September in HP's dvd100i) lets users record, erase and re-record video onto discs that can be played on any typical DVD player. On January 30, HP Labs honored the research team behind this technology.

an impossible task?

A little background on optical recording may explain why researchers faced such a difficult technical problem. At the time, many believed it would be impossible to make a rewritable disc that could play on a conventional DVD player.

Here's why: Writable discs and music/video discs are made quite differently.

"Suppose you've typed part of a document on one typewriter and removed it from the machine," explains researcher Craig Perlov. "Later, you decide to add to it or change what you've written. If you put the sheet back into the typewriter (or worse, in a different typewriter) you can never get the paper lined up just right -- there is always some misregistration between new type and the old."

Quote: 'At the first meeting, they were humoring us because HP was a good customer, and the naive labs team thought they had a good idea.  By the second meeting they were listening, looking at their data, shaking their heads and genuinely impressed

no room for error

A similar phenomenon happens with discs. Recordable discs, like other writable mass storage products include gaps (often called link blocks) between blocks of data. These link blocks allow the drive to resynchronize itself between the new data and previously written data.

Conventional DVD players don't know what to do with the link blocks. The DVDs you buy in the video store are molded, not written in a computer, without the link blocks. They are designed not to be copied.

On music/video DVD, the space between data bits is 133 nanometers -- less than 1/100th the width of a human hair. So when merging new data with old, misplacing bits by even 60 nanometers can make the information on the disc unreadable.

Creating a disc that was writable but could still be read by standard DVD players presented the researchers with a thorny technical problem. They had to figure out how to pulse a laser onto a disc spinning at three meters per second at exactly the right moment so that it would create a mark of exactly the right length on the disc surface. That mark had to be exactly the right distance from the previous mark.

solving the problem

For inspiration, the team called itself SPOT, to focus on the idea of a laser hitting a spot on a disc. Researchers adopted an image of a Dalmatian then being used in HP's LaserJet ads as their mascot, with a nod to Nipper, the famous RCA dog.

The research team -- which over its course included Danny Abramovitch, Ilkan ,okgsr, Mina Farr, Mike Fischer, Mitch Hanks, Dale Hill, Josh Hogan, Terril Hurst, Craig Perlov, Carl Taussig, Dave Towner and Carol Wilson -- solved the problem by exploiting the geometric characteristics of the disc surface.

Information on a disc is organized onto a track that spirals around the disc. On writable discs, these tracks are defined by grooves similar to a phonograph record. The grooves often have a wave-like wobble perpendicular to the ridges used for address information (to identify the tracks).

linking old data with new data

The researchers hypothesized that by increasing the frequency of the wobble, they could use it as a timing reference for pulsing the laser, thereby enabling "linkless editing."

Linkless editing is the ability to write a new block of data and link it with the previous block without any glitches in the timing or phase of the data. It is the key to playback in standard DVD players. Two researchers, Abramovitch and Towner, were awarded a patent for their "high-frequency wobble" approach in 2000.

The next step was to turn it into a product for HP. In April 1998, HP presented its ideas to an alliance of optical recording companies, including Philips, Sony, MCC, Yamaha and Ricoh. These companies, all seasoned veterans in optical recording technology, were highly skeptical of HP's concepts.

dazzling the doubters

"I clearly remember the attitude of one partner's team, and how it changed from the first meeting to the second," says Marvin Keshner, who was then director of the lab and center where the researchers worked. "At the first meeting, they were humoring us because HP was a good customer, and this 'naive' Labs team thought they had a good idea.

"By the second meeting, they were listening, looking at their data, shaking their heads and genuinely impressed."

The Labs team overcame repeated technical challenges to produce a prototype of the entire assembly, including the spinning mechanism, signal processing algorithms and recording system. They designed numerous test discs that were prototyped by Mitsubishi Chemical Corporation.

turning out a product

By 1999, the system was robust enough for production, and in September 2001, HP released the dvd100i, one of the the world's first commercially available DVD+RW systems compatible with most DVD players. (Ricoh relased the other simultaneously). HP also developed equal-share licensing agreements with Sony and Phillips, so that the three companies share royalties for any DVD+RW product in this format sold by another company.

(A competing rewritable format, DVD-RW, is considered less versatile. According to the DVD+RW Alliance, an industry group that includes HP, DVD+RW is the only rewritable format that provides full, non-cartridge, compatibility with existing DVD-Video players and DVD-ROM drives for both real-time video recording and random data recording across PC and entertainment applications.)

research team honored

Because HP decided to outsource the manufacturing of its CD-RW and DVD+RW systems, the research team ceased work on the technology after the transfer to production.

In January, however, the members of the research team still with HP Labs -- Perlov, Hurst and Taussig -- received the third annual Joel S. Birnbaum Prize for Innovation. The prize, named for a former HP Labs director, honors an HP Labs employee or team whose contributions demonstrate "extraordinary vision, innovation, creativity, and perseverance."

by Hazen Witemeyer and Jamie Beckett


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photo: Terril Hurst, Craig Perlov, Carl Taussig receive their award from Joel Birnbaum
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