An Introduction to DVD Recordable (DVD-R)DVD Recordable (DVD-R) technology allows anyone to create DVD disks at the desktop. Similar in concept to Compact Disk Recordable (CD-R), DVD-R is a write-once medium that can contain any type of information normally stored on mass produced DVD disks - video, audio, images, data files, multimedia programs, and so on. Depending on the type of information recorded, DVD-R disks are usable on virtually any compatible DVD playback device, including DVD-ROM drives and DVD Video players. A DVD-R disk is able to contain a maximum of either 4.7 or 3.95bn bytes of information on each side, depending on the type of blank media used. Since the DVD format supports double-sided media, up to 9.4Gb can be stored on a single double-sided DVD-R disk. Data can be written to a disk at a DVD "1X" equivalent of 11.08Mbit/s, which is roughly equivalent to nine times the transfer rate of CD-ROM's "1X" speed. After recording, DVD-R disks can be read at the same rate as mass-produced replicated disks, depending on the "X" factor of the DVD-ROM drive used. These transfer rates, coupled with DVD-R's capacity and conformance to worldwide DVD standards, makes it an extremely viable and cost effective storage medium. DVD-R Technology DVD-R is a write-once format, meaning that data can be written to a disk and stored without fear of accidental erasure. The fundamental technology employed is similar to that used by CD-R, except that data is written at a higher rate and density. DVD-R, like CD-R, uses a constant linear velocity rotation technique to maximise the storage density on the disk surface. This results in a variable number of revolutions per minute (rpm) as disk writing/reading progresses from one end to the other. Recording begins at the inner radius and ends at the outer. At "1X" speeds, rotation of the disk varies from 1,623 to 632rpm on 3.95Gb media and 1,475 to 575rpm on 4.7Gb media, depending on the record/playback head's position over the surface. On 3.95Gb media, the track pitch, or the distance from the centre of one part of the spiral information "track" to an adjacent part of the track, is 0.8 microns, one-half that of CD-R. 4.7Gb media uses an even smaller track pitch of 0.74 microns. DVD-Recordable Disk DimensionsTo help achieve a six to seven-fold increase in storage density over CD-R, two key components of the writing hardware needed to be altered: the wavelength of the recording laser and the numerical aperture (NA) of the lens that focuses it. With CD-R, an infrared laser with a wavelength of 780 nanometers (nm) is employed, while DVD-R uses a red laser with a wavelength of 635nm. At the same time, the numerical aperture of a typical CD-R drive's objective lens is 0.5, while a DVD-R drive uses lenses with a NA of 0.6. These factors allow DVD-R disks to record marks as small as 0.40µm as compared with the minimum 0.834µm size with CD-R. Recording on DVD-R disks is accomplished through the use of a dye recording layer that is permanently transformed by a highly focused red laser beam. This dye substance is spin-coated onto a clear polycarbonate substrate that forms one side of the "body" of a complete disk. The substrate is injection moulded, and has a microscopic, "pre-grooved" spiral track formed onto its surface. This groove is used by a DVD-R drive to guide the recording laser beam during the writing process, and also contains recorded information after writing is completed. An undulating "wobble" signal is moulded into the pre-groove for synchronising a DVD-R drive's spindle motor during the writing process, and "Land Pre-Pits" (LPP) are also contained in the land areas between grooves for addressing purposes. A thin layer of metal is then sputtered onto the recording layer so that a reading laser can be reflected off the disk during playback. A protective layer is then applied to the metal surface, which prepares the side for the bonding process. These steps are done for each side of a disk that will be used for recording. If only a single recording side is required, then the opposite side can contain a label or some other visible information such as pit art. If both sides are needed for recording, then two recordable sides can be bonded together. In this case each side must be read directly by flipping the disk over, as dual layer technology is not currently supported. The recording action takes place by momentarily exposing the recording layer to a high power (approximately 8-10 milliwatt) laser beam that is tightly focused onto its surface. As the dye layer is heated, it is permanently altered such that microscopic marks are formed in the pre-groove. These recorded marks differ in length depending on how long the write laser is turned on and off, which is how information is stored on the disk. The light sensitivity of the recording layer has been tuned to an appropriate wavelength of light so that exposure to ambient light or playback lasers will not damage a recording. Playback occurs by focusing a lower power laser of the same approximate wavelength (635 or 650nm) onto the surface of the disk. The "land" areas between marks are reflective, meaning that most of the light is returned to the player's optical head. Conversely, recorded marks are not very reflective, meaning that very little of the light is returned. This "on-off" pattern is thereby interpreted as the modulated signal, which is then decoded into the original user data by the playback device. Expected Life of DVD-R Media Life expectancy is a key issue when considering the use of DVD-R for applications such as document imaging and other archival applications. Although each disk media manufacturer has its own life expectancy rating, Pioneer DVD-R media is currently rated at better than 100 years. Compatibility Properly recorded DVD-R disks should be playable on nearly any destination device that can properly make use of whatever data is written. Recorded DVD Video disks can be played on a DVD video player, as well as a computer that is equipped with a DVD-ROM drive, a DVD-compliant MPEG decoder card (or decoder software) and application software that emulates a video player's control functions. A recorded DVD-ROM disk can be read by a computer equipped with a DVD-ROM drive, as well as a computer equipped for DVD video playback as described above. DVD Video components are not necessary, however, if DVD Video material is not accessed or is not present on a disk. Recorded DVD-R disks support a new file system called "UDF Bridge". This is a hybrid approach that provides both the newer UDF (Universal Disk Format) system as well as the older ISO-9660 system used by the CD-ROM format. This allows DVD disks to be used with computer operating systems that do not have any provision for UDF support. Recording a Disk The basic recording process for DVD-R disks should be familiar to any user of CD-R technology. Like CD-R, blank DVD-R disks are recorded in a DVD-R drive that is controlled by a host computer. The recording process is orchestrated by application software that allows a user to specify which files will be transferred to the disk as well as conducting the actual recording itself. All DVD disks, recordable or not, must have three basic areas recorded on them: lead-in, user data and lead-out. The lead-in and lead-out areas are boundaries that indicate to a playback device where the inner and outer limits of a recording are respectively. They contain no user accessible information, but are critical to the proper functioning of a disk. There are two methods of writing a DVD-R disk: disk-at-once and incremental writing. Disk-at-once, as its name implies, is the process of writing an entire disk's worth of data, up to 4.7Gb, at one time. A host computer must consistently provide data at a full 11.08Mbit/s during any recording to avoid buffer under-run errors. Buffer under-runs can be minimised by the use of a large writing buffer memory in a DVD-R drive; Pioneer's second generation drive in fact provides a 6.75Mb buffer that can absorb bit stream interruptions of more than four seconds in duration. As faster writing speeds are developed in future products, host computer performance and drive buffer requirements may also need to increase accordingly. DVD-R disk-at-once writing is performed such that the lead-in, data area and lead-out areas are all written sequentially. This differs from how CD-R disks are typically written, where the data area is written first, followed by the lead-in/table of contents and lead out areas. Disk-at-once recording is likely to be used when authoring video titles due to the large size of these programs. It can also be used for multimedia or other software titles intended for publishing, as these works are normally assembled on hard drives as a finished image file prior to testing them on DVD optical disks. Incremental writing is also supported by the DVD-R format. This is very similar in concept to the packet writing technology that is used with CD-R. Incremental writing allows a user to add files directly to a DVD-R disk one recording at a time instead of requiring that all files be accumulated on a hard disk prior to writing as with the disk-at-once method. The minimum recording size must be at least 32Kbit, (even if the file to be recorded is smaller) as this is the minimum error correction code (ECC) block size for DVD. A disk that is being written to incrementally cannot be considered a complete volume until the final information has been stored or the disk capacity has been reached. The lead-in and lead-out boundary areas therefore cannot be written until either of these two events occur. Such an "unfinalised" disk (one without lead-in, lead-out and complete file system data) can only be read by a DVD-R drive until this process can be completed. After finalisation, a destination playback device can then read a disk, but data can no longer be added to it. Recording Platform Pioneer has made successful recordings onto DVD-R disks using a host computer system comprised of the following components: Pentium 100 PC or better Windows NT 4.0 or Windows 95/98 operating systems (software dependent) Premastering application software Adaptec 2940 SCSI host adapter 9Gb hard drive Pioneer external SCSI-2 DVD-R drive This configuration represents a modestly powerful computer system containing no exotic components and should be relatively easy for a typical user to assemble. Time to record one disk A complete 3.95Gb side is written in approximately 50mins in a disk-at-once recording, regardless of the data that will be contained. A 4.7Gb disk can be fully written in approximately one hour. Even variable bit rate MPEG video data is recorded at the full 11.08Mbit/s rate. Upon playback, a video player accomplishes the necessary bit rate variation with a buffering technique. All information, video or otherwise, is written at the full 11.08Mbit/s data rate, with playback equipment providing any necessary time base adjustments. DVD-R Applications DVD-R's relatively low cost per megabyte, coupled with its physical storage efficiency and the portability of its recording equipment makes the medium applicable to a large variety of uses in virtually all industries. There are three fundamental applications anticipated for DVD-R: Testing and development Distribution Storage and archival Testing and development Many DVD applications utilise replicated read-only disks that are mass-produced and distributed to a large number of users. Preparation of the content that will be published can be a complex and time consuming process that must be completed accurately to avoid errors or functional defects. Compared with the cost of the mastering and set-up efforts required to replicate only one disk, DVD-R provides a far more cost effective method of testing content prior to mass production. A single low cost disk can be quickly written and tested in a representative destination device (video player or ROM drive). In fact, multiple test disks may be required throughout the development process, as published titles are often the collaborative effort of many people. As a result, DVD-R media can make a significant contribution to reducing the cost of DVD publishing. The relatively recent achievement of 4.7Gb capacity on DVD-R media has helped to realise parity with DVD-5 replicated disks. This allows both qualitative and functional testing of titles that will utilise the full capacity of mass-produced media - a substantial issue in the DVD video authoring world. Distribution DVD-R's low-cost media and relatively portable recording equipment can aid small-scale distribution of DVD content. As in the testing example above, mastering and replication expenses can be prohibitive when only a single disk or very small quantity is required. DVD-R allows disks to be recorded at the desktop level, which can result in very quick turnaround and significantly lower cost. Some users may not be comfortable with sending sensitive data files or other work in progress to an outside facility for replication, so the ability to maintain continuous in-house control of this information can be crucial. This is particularly true with classified data maintained by Government agencies. Complete confidentiality is afforded by DVD-R because it can easily be maintained as a completely in-house process. Storage and archival DVD-R media provides archival lifetimes that are equal to or better than CD-R; Pioneer media is rated at greater than 100 years. For this reason, the format is suitable for long-term archival of any information that can be stored digitally. This includes image data, film and video archives, or any other media that need to be retrieved more easily by users. In fact, DVD-R's much larger capacity makes it especially suitable for large image files that do not fit onto a single CD-R volume, thus creating new opportunities for inexpensive storage of these assets. High-resolution satellite images are an example of very large files in excess of 1Gb each. Since DVD disks are dimensionally identical to the CD family of disks, they have the advantage of being compatible with existing CD-based jukebox and changer mechanisms. This allows automated retrieval of recorded DVD-R volumes in networked environments, with a six to seven-fold increase in storage density as compared with CD-R technology. As an example of how DVD-R can reduce overall archival system costs, a 100-disk DVD-ROM jukebox can contain a total of 470Gb, or nearly a half-terabyte of data. If 50Kbit image files are written on every disk, a total of 10m images can be stored and retrieved in a single, compact device. Using CD-R, seven of the same jukebox mechanisms would be required to maintain the same disk-to-drive ratio, which significantly adds to the system cost. Conclusion In essence, DVD-R disks can be thought of as enormous "bit buckets". Any kind of digital data can be stored on them, such as high quality video databases, motion pictures, document images, audio recordings, multimedia titles, and so on. The format's high capacity and data transfer rate has the potential to expand existing CD-R applications in two dimensions: faster information flow (i.e. higher quality video), as well as significantly more data on each volume. DVD Recordable provides users with a powerful new tool that has applications in nearly every industry. Pioneer believes that DVD-R is the next logical step forward from the very successful CD-R format in applications that benefit from write-once security but inevitably require more capacity. As DVD technology takes its place as the eventual replacement for the ubiquitous CD, DVD-R will become an indispensable medium that can be counted upon to store and deliver digital information reliably and inexpensively.
This was first published in July 1999