DVD recordable field................................................
It should come as no surprise to anyone with a nodding acquaintance with the removable data storage industry that someone is always coming up with a newer, bigger, better, faster technology. It is as traditional for these technologies to be proprietary as it is for them to be mutually incompatible. The removable optical offerings in this market have historically been no different from their magnetic counterparts, leapfrogging each other in speed and capacity and positioning themselves for comfortable niches where they can dominate a particular application.
Few of the non-CD-based optical options give a second or even a first thought to interchangeability at even the lowest level. Compact discs, certainly, have been a notable and extremely successful exception to this rule. The compact disc family of data storage technologies has built upon the success of what originated as a read-only data delivery format, to produce both recordable and rewritable versions, all the while attempting to maintain at least a semblance of compatibility.
This incompatibility rule does appear to be changing. One early example of this is the Matsushita PD drive, which reads CD-ROM, but also reads, writes, and rewrites a proprietary phase-change cartridge of the same capacity and similar form factor as CD-ROM. When CD-RW was introduced in 1996, some industry analysts decried the new rewritable compact disc technology as a violation of the CD tradition of compatibility, since existing CD-ROM drives could not read the new CD-RW media. Fortunately, only minor and inexpensive changes are needed to make CD-ROM drives capable of reading CD-RW media; these alterations, called MultiRead, are already widely implemented in CD-ROM drives being produced today.
The trend towards multifunction removable storage is most evident in some of the candidates for future high-density rewritable optical formats. The high expectations for DVD as the pervasive read-only data delivery successor to CD-ROM's huge installed base are already being applied to DVD-based DVD-RAM and DVD+RW. But these expectations are also spawning non-DVD-based formats that are capable of reading DVD. In anticipation of the projected success of DVD, no fewer than four emerging technologies--so far, at least--promise to offer additional playback platforms for DVD, as well as other CD-based formats, while simultaneously offering the capability of recording and rewriting high volumes of all types of data, including--but not limited to--DVD Video.
No one who follows CD-ROM believes this format's success is based solely and squarely on its technical merits, but rather, understands that market forces, business opportunities, and cost advantages have played important roles in the compact disc story, just as the matter of pursued market share, potential revenue streams, and even the clash of corporate cultures among several of the world's largest technology and media companies provided a foundation for the fights over earlier high-density CD specifications that resulted in DVD.
As the world continues its unstoppable march toward all things digital, the stakes get ever higher. In the world of high-density rewritable optical platforms, you can bet that politics plays as much a role as bits and bytes.
The fact is, rewritable optical technology isn't just for data storage anymore. Sony's Minidisc, introduced in 1992 for recording and distributing consumer audio, did not enjoy the same success in the U.S. as it did in Europe and Japan, although it has lately experienced something of a renewal of interest, as well as a reduction in price. Pioneer offers a consumer audio CD Recorder, and Philips' new CD-RW home audio recorder was recently featured in a full-page color ad in the Wall Street Journal. Can a high-density rewritable optical consumer device for digital video be far behind?
THE CONTENDERS: DVD-RAM, DVD+RW, MMVF, ASMO, AND MORE?
Although the role of the digital video replacement for the VCR looks like a starmaker, the assumption that this position will be filled by technology based on DVD is not well-founded. DVD may or may not achieve primacy as the standard digital video delivery medium, but its recordable and rewritable versions are not necessarily appropriate for this application.
The biggest and most obvious drawback is the current DVD-RAM and DVD+RW formats' low capacity compared to DVD-ROM. But even more restrictive is the very nature of the DVD Video format, which is far more complex than an MPEG-encoded data stream, and requires a DVD-Video subsystem to decrypt and decode video and audio and to process DVD-Video navigation and presentation instructions. Another looming factor is pending copyright legislation that could render the whole issue of consumer recordable digital video moot.
If the requirement of rewritable media being readable on a DVD-Video player were ruled out--in deference to what video content owners would no doubt prefer--a digital video counterpart of the VCR is not only technically feasible, but even attractive. For example, by combining a real-time MPEG-1 encoder with a rewritable optical drive and medium, and with NTSC playback capability, you would have the ability to record 83 minutes per gigabyte of VHS-quality video (at about 1.6Mb/s) and play it back on a standard television. Give this device an MPEG-2 encoder, at 5Mb/s data stream sizes, and the video quality approaches laserdisc, although the video capacity goes down to 26 minutes per gigabyte. On DVD-RAM's 2.6GB, that's a little more than an hour, but on ASMO's five to six gigabytes, it's long enough for a two-and-a-half hour movie. Fall back to MPEG-1, and the 83 minutes per gigabyte on ASMO has sufficient capacity to record over eight hours of (arguably) good-enough quality video. A few bells and whistles would even provide a menu for instantaneous access to program points, as well as the ability to jump to different places on the disc and avoid the fast-forwarding through a VHS tape suffered by many today.
Even if rewritable high-density optical formats are being considered in the long term as VCR replacements by some companies, there are many factors that need to be considered, including cost and consumer interest. Besides which, high-density rewritable discs making any dent in the VHS hegemony is hardly guaranteed. Today, DVD-RAM and DVD+RW are seen as computer peripherals, while NEC's MMVF--as the name, Multimedia Video Format, suggests--may be setting its sights sooner on time-shifting consumer video recording. ASMO's more immediate goals and long-term hopes are less clear.
DVD-RAM, Forum Approved
DVD-RAM is a mixture of storage methods from magneto-optical [MO], phase-change [PD and CD-RW], and even magnetic hard drives. DVD-RAM, for DVD Random Access Memory, is the "official" DVD Forum-approved format. DVD-RAM was the subject of a year-long behind-the-scenes battle among the members of the DVD Forum, the ten company group that jointly defined the specifications for DVD-Video and DVD-ROM. DVD-RAM's principle architects and backers are Matsushita Electrical Industrial Company, Toshiba Corp., and Hitachi, Ltd., all three of whom have announced DVD-RAM product availability by early 1998. A DVD Forum-sponsored DVD-RAM briefing at San Jose's Fairmont Hotel on September 15, 1997 provided an early view of products from the three companies. While Toshiba is sampling SCSI-2 and EIDE drives now for prices between $300 and $500, and Hitachi has plans for sampling in the fourth quarter for internal and external drives for $794 and $953, respectively, Matsushita has yet to offer drive samples or pricing information.
The technical specifications and diagrams for DVD-RAM are somewhat bewildering, at least at first glance. DVD-RAM is a mixture of storage methods from magneto-optical (MO), phase-change (PD and CD-RW), and even magnetic hard drives. Some of the methods being used in DVD-RAM are seeing their application debut, but even the ones that have appeared in previous technologies have never been combined in one format. As a result, DVD-RAM is directly comparable to nothing that has come before and requires an understanding of not just basic and traditional optical storage technology, such as MO and CD-R, but of new developments that have never been used before in actual products.
DVD-RAM holds 2.6GB per side, uses phase-change as a recording material, the "wobbled land and groove" recording method, embossed pits for header (addressing) information, and Zoned Constant Linear Velocity (ZCLV) rotational control, and is a random-access, non-sequential medium. DVD-RAM-compatible readers will require servos to handle switching between the lands and grooves. DVD-RAM drives will also need a decoder to handle scattered 32K ECC Blocks, something not needed for DVD-ROM and DVD+RW, since their blocks are contiguous.
So far only five companies have made experimental DVD-RAM media. This media will resemble MO, complete with "hash marks" of the embossed areas and zone demarcations, and DVD-RAM media must be certified by the manufacturer to establish a Primary Defect List. The media will require a cartridge: a Type One cartridge can hold either a two-sided or one-sided disc and the disc may not be removed; Type Two cartridges have been defined as holding a one-sided disc that may be removed to be read on DVD-ROM readers that may be designed in the future to read DVD-RAM. One problem for DVD-RAM, however, is that removing the media from the cartridge may compromise rewritability. And depending on the choices left to drive manufacturers, a DVD-RAM drive may or may not read CD-R, CD-RW, or PD.
DVD+RW, Plus or Minus?
DVD-Rewritable, or DVD+RW, as the sponsoring companies call it, is supported by Sony, Philips, Hewlett-Packard, Ricoh, Yamaha, and Mitsubishi. Capacity is 3GB per side, and the disc uses phase-change, groove-only recording like CD-RW. Other characteristics include the use of CAV wobble for addressing and CAV or CLV rotational control for providing a choice between raw data transfer and faster data access. DVD+RW can be a sequential medium like CD+RW and CD-ROM, or a random-access storage device.
DVD-RW, it is widely supposed, can be read on future DVD-ROM readers that implement only minor hardware changes; these changes would include a different decoder to handle link frames and firmware for data loading at initialization. A DVD+RW drive will be able to read CD-ROM, CD-R, and CD-RW media, as well as DVD Video and DVD-ROM.
The media looks just like CD- or DVD-ROM and does not require a cartridge, although, as with CD-ROM media, a caddy is an option for "extreme environments"--those that are particularly unfriendly to rewritable media due to dust, dirt, or constant handling. No manufacturer certification is required for defect management at the media plant, but it is an option for companies who require pre-certified media.
Although none of the DVD+RW companies have made product announcements to date, best estimates place the arrival of actual DVD+RW products no sooner than summer 1998.
ASMO Advances MO
ASMO is an acronym for Advanced Storage Magneto-Optical, but, as if to further confuse the industry, had been referred to as MO7 during much of its development. ASMO grows out of the work of the Advanced Storage Technical Conference (ASTC), which formed with the intention of defining and developing a new high-speed, random-access, direct overwrite-rewritable, optical system specification using magneto-optical (MO) technology. ASTC Executive Committee members include Fujitsu Ltd., Hitachi Ltd., Hitachi Maxell Ltd., Imation Corporation, Olympus Optical Co. Ltd., Philips Electronics NV, Sanyo Electric Co. Ltd., Sharp Corporation, and Sony Corporation. The ASMO working group members include Highwits Technology, Mitsubishi Chemical, Matsushita Electrical Industrial Co., Tosoh Corporation, LSI Logic Corporation, and LG Electronics.
ASMO represents not just an advance in MO capacity and functionality, but a move towards lower-priced MO technology for desktop removable storage. ASMO is direct-overwrite magneto-optical, and holds either 5GB or 6GB per side, depending on formatting. ASMO drives are expected to be capable of reading CD-ROM and DVD-ROM with a specified 650nm laser and the right signal-processing circuitry, although ASMO media will not be readable on DVD and CD players and drives; without drives available, it remains unclear whether ASMO drives will be able to read CD-R and CD-RW. The drives will require a cartridge for the media.
ASMO discs can be formatted into 2KB sectors for ZCAV (Zoned Constant Angular Velocity) access, which provides 5GB of capacity, or into 32KB sectors and ZCLV (Zoned Constant Linear Velocity) access, for 6GB capacity. ASMO's ZCAV format makes the device more adaptable to random-access data, while the ZCLV format is better-suited for streaming audiovisual content.
One intended use of ASMO drives is as auxiliary high-volume storage systems for personal computers, and some industry observers believe that the proposed devices are potentially viable substitutes for hard drives. Another compelling use for ASMO could be as a platform for DVD title development, including linear and non-linear video editing, image archiving, and MPEG-2 and AC-3 video and audio encoding, with the removable ASMO media a likely candidate as input media for DVD replication. Other anticipated PC applications include archival storage, network server data storage, and high-performance desktop publishing, while video production uses, such as electronic news gathering and digital video storage for camcorders and even consumer video recording systems, are being considered.
Version 0.9 of the ASMO specification was finalized by the ASTC in June 1997. ASMO, like other MO media, is capable of tens of millions of rewrites, in comparison to DVD-RAM's estimated 100,000 rewrites. Other ASMO advantages, according to its boosters: ASMO can reach higher transfer rates and faster access times. But perhaps the biggest advantage seen for ASMO is the format option for sequential data storage--like audio or video data--that eliminates the manufacturing requirement of certification for defect management, which is not an option for DVD-RAM media manufacturing.
No ASMO products have been announced to date.
MMVF, Multimedia Video Focus
MMVF, which stands for Multimedia Video Format, is supported by NEC, and is a phase-change media with a capacity of up to 5.2GB per side. MMVF uses land and groove recording and 1,7 RLL encoding (DVD+RW and DVD-RAM use 8-16 modulation, or 2,10 RLL, like DVD-ROM). The MMVF drives will read "CD-ROM family," although how extensively this family is covered remains unknown, with questions still pending regarding various recordable and rewritable members of the CD/DVD clan. Also still pending is whether or not MMVF will require the use of a cartridge.
MMVF is still in the category of defined, but not produced or announced in product form.
Different Formats, Common Parameters ... But Other Possibilities, Too
However the specifications--to the extent they are known--for DVD-RAM, DVD+RW, ASMO, and MMFV may differ in detail, they share many common parameters, such as form factor, at 12cm, laser wavelength, at 650nm, and numerical aperture, at 0.6. These basic similarities are important factors in interchangeability. For instance, no matter how alike two types of media might be in terms of content, a five-inch disc just won't fit in a three-inch form factor drive. Not coincidentally, these common specifications are what make compatibility with read-only DVD possible, at least as far as replicated DVD discs playing in rewritable drives are concerned. When it comes to compatibility between and among DVD-RAM, DVD-R, DVD+RW, ASMO, and/or MMVF, the jury is still out. Actually, with few drives available--or even in existence--for cross-compatibility testing, and little or no media around, the jury hasn't even been impaneled yet.
And then there is the product of research labs and rumor mills, with such things as reports of blue laser advances, suggesting--insisting, according to certain analysts and, for that matter, the weight of technological history--that further advances in data storage are not only coming, but perhaps are closer than many may think. When it comes to prognosticating high-density rewritable optical formats, the point isn't that new technological strides won't happen, but rather, that market conditions today, such as conflicting formats and the probable result of product release delays, may shift the market's focus forward to yet other formats not out of the lab today.
But what can be determined about how DVD-RAM, DVD+RW, MMVF, and ASMO use some of the same advanced techniques and technologies, and whether these advantages promote compelling arguments for one, or even all these formats? Understanding these factors can go a long way toward assigning the right balance between technological superiority and market-making factors, such as first-to-market advantages, intellectual property gains, and the public's perception concerning these various formats' strengths and weaknesses in particular applications.
NEW TECHNOLOGIES, NEW TECHNIQUES, NEW FORMATS YET TO COME?
The four proposed formats, far from being the last word in optical storage, may augur of more yet to come. The emergence of new high-density optical storage formats is not simply the result of the creation of DVD, but rather the sign of much larger forces.
Since the 1980s, Japanese companies have been steadily increasing investments in research and development in optical storage technologies, to the point where Japan's optoelectronics business is worth $40 billion in annual sales, compared to total annual U.S. optoelectronic sales of $6 billion, even though many of the major users of optical storage technology are located in the United States. According to Japan's MITI (Ministry of International Trade and Industry), "Electronics is the science of the twentieth century, and optics is the science of the twenty-first." DVD can be seen as only one of the fruits of these labors and this philosophy.
The emerging high-density optical storage formats have been made possible by a collection of various new techniques. The formats are differentiated, not so much by their proposed applications, but by how these techniques are combined in unique ways. Most of the new techniques are designed for increasing capacity, rather than improving seek times and data rates. According to Optoelectronics In Japan And The United States, a report by the Japanese Technology Evaluation Center (JTEC), published in February 1996, "[Increasing capacity] might be an indication of a lack of cost-effective solutions to improving the speed of optical disk systems, but it may also indicate that Japan's optical storage industry is focusing on multimedia and entertainment applications with modest speed requirements, thus leaving the mainstream computing applications to magnetic hard disk drives."
Picking Up the Land/Groove Recording Groove
Those accustomed to recordable compact disc technology, which uses a single wobbled spiral pregroove track to guide a recording laser, may find land/groove recording new and different. But in fact, land/groove technology was originally developed and used for magneto-optical media. In traditional MO media, the information is recorded on the land area, the grooves are used as a tracking guide, and they appear as two parallel spirals. Keeping the lands separated by grooves eliminates crosstalk between adjacent tracks. The use of land/groove technology is one of the differentiating elements that separates DVD-RAM, MMFV, and ASMO from DVD+RW.
see part II |
