DVD-RAM Bridges Gap Between Requirements And Expectations.
In 1999, the DVD Forum published the DVD-RAM Book 2.0 with the specification for the new 120mm 4.7GB per side DVD-RAM Format. The increase from 2.6GB to 4.7GB was accomplished by specifying low noise media and by defining a new adaptive write strategy. Besides these two areas, all format features of the initial DVD-RAM standard are maintained:
* Track Format. Wobble Land and Groove-high reliability. ZCLV-Large capacity and high speed access.
* Addressing Scheme. Wobble Linked ID-High address reliability.
* Sector Format. DVD-ROM compatible ECC block-16 sectors.
* Recording Scheme. Polarity and Data Position Randomization-High overwrite durability.
While the initial 2.6GB DVD-RAM disc was accepted as a removable data storage device, the new 4.7GB format Features significant enhancements, which will increase the use in video recording and multimedia applications:
* Modified Defect Management Scheme. Provides large recording area without discontinuities; accommodates bare disc use; enables drop-in video recording.
* Media Identification. Enables disc-based copy protection.
In February 2000, an 80mm disc was introduced with version 2.1 of the DVD-RAM standard. This new form factor is targeted at consumer devices such as camcorders, Internet appliances, and small form factor PCs.
A comparison of the new 4.7GB DVD-RAM specification with the DVD-RAM Book 1.0 and DVD-ROM shows how much current DVD technology is used to arrive at a compatible 4.7 DVD-RAM solution (Table 1). By employing an enhanced media structure and adaptive recording algorithms, the new 4.7GB DVD-RAM media format provides single-layer capacities matching DVD-ROM. By maintaining the physical surface layout with wobbled land and groove features, this format maintains DVD-RAM's high address reliability and data integrity.
In February 2000, version 2.1 of the DVD-RAM standard was released introducing an 80mm disc. This new form factor is targeted at consumer devices such as camcorders, computing appliances, and small form factor PCs. Like the 120mm version, the 80mm DVD-RAM disc is available with an optional cartridge for maximum data protection (Table 2).
Main Media Features
The higher recording density of a 4.7GB DVD-RAM disc s achieved by using improved media featuring a contrast enhancement layer. This layer improves the reflectivity contrast between recorded and unrecorded regions, resulting in high signal-to-noise ratios. An additional thermal buffer layer, added to the disc composition, enables homogenous heat absorption at the recording layer level, which allows precise edge control of the recorded marks on the disc. These two new media layers allow increased area density without compromising data liability and integrity.
Adaptive control algorithms control the position and width of the first and the last recording pulse. The algorithm determines pulse width and position variation with respect to the length of the data marks and surrounding spaces, ensuring a uniform thermal profile during the post recording cooling process.
DVD-RAM Book 1.0 was developed with an integrated defect management scheme that allows for a defect free user data space. The defect management scheme provided data structures to aid initial media certification and the allocation for defect growth over the lifetime of the media. This way of dealing with media imperfections and contamination has been proven successfully in computing environments. However, to obtain sufficient data access times, drives must feature fast seek mechanisms that may be more costly to produce than the mechanisms of low cost consumer video players.
Real-time video recording and playback are the most important applications for DVD-RAM discs in the consumer space. However, low cost DVD-RAM drives may have insufficient access performance to maintain a stream of video data. To allow the use of 4.7GB DVD-RAM media for video recording, Book 2.0 introduced some subtle changes to the defect management scheme of Book 1.0.
Book 1.0 defined a surface layout that used local spare areas in each zone. For video recording applications, the local spare areas represent a discontinuity in the video data stream that may cause video drop-outs when the video is played back on a low cost video player. In order to avoid playback interruptions, streaming data should be arranged continuously on the disc. To obtain the largest uninterrupted data recording area, Book 2.0 redefined the surface layout. The new layout allowed slightly modified data structures to be used and to maintain FW algorithms that have been developed for 2.6GB drives. This new layout allows DVD-RAM discs to function optimally in both computer and video environments.
Defect Management-Spare Area Allocation
Book 2.0 defines two methods for replacing defective sectors with a good one. The first one, Slipping Replacement, is a method in which a defective physical sector is replaced by the first good physical sector immediately following the defective sector. Defective sectors replaced by the slipping algorithm are listed in the Primary Defect List (PDL), which is recorded in the Defect Management Area (DMA) on the DVD-RAM media during formatting.
Linear Replacement is the second method. This method is used when a defective sector is encountered during read/write operations. A defective sector is replaced with a good one in a separate spare area. This imposes seek and rotational latencies that may cause video drop-outs. Defective sectors replaced by Linear Replacement are listed in the Secondary Defect List (SDL), which is recorded in the Defect Management Area (DMA) on the DVD-RAM media during normal operation.
While the two defect management methods of Book 2.0 are identical to Book 1.0, Book 2.0 defines a new Primary Spare Area (PSA) and a new Supplemental Spare Area (SSA) that achieve the goal of maximizing an uninterrupted recording area. The PSA is reserved as a spare area for all primary defects and some secondary defects. The PSA has a fixed size of 26MB. The SSA is used for defects found during normal operation of the disc once the PSA is full. The size of the SSA can be changed from 0 to a maximum of 200MB. The SSA may be allocated during formatting to accommodate different operating modes:
* The disc may be initialized without a SSA for real-time video and audio recording and use of a cartridge.
* The disc may be initialized with a SSA when used in dusty environments or when used without a cartridge.
* The SSA may be expanded during use.
Defect Management-Slipping Replacement
Primary defects found during disc formatting are registered in the Primary Defect List. The user area expands into the Primary Spare Area.
Defect Management-Linear Replacement
Secondary defects found during normal operation are registered in the Secondary Defect List. Defective sectors are replaced with PSA sectors until the PSA is full. Then spare sectors in the SSA will be used.
Drop Recording is a simple solution to implement real-time recording in the PC environment. The PC records a video stream through defects rather than going to their respective replacement sectors. This way no latency is incurred. Drop-outs during playback are accepted.
While performing drop recording, the recording device updates the Status of Linear Replacement (SLR) flag to indicate that a known secondary defect has been ignored and has not been replaced with its assigned spare sector. This flag is needed to maintain the integrity of the defect management scheme.
Burst Cutting Area
The DVD-RAM Book 2.0 introduces a Burst Cutting Area (BCA) that is part of the disc Lead-in area. This feature is identical to the DVD-ROM specification. The BCA may be used to provide individual numbering for DVD-RAM discs, which may be used as a unique disc key in a content scrambling or encryption scheme.
With the introduction of DVD-RAM Book 2.0, the concept of a single rewritable DVD format for AV and PC usage has become a reality. With the release of these specifications, the DVD-Forum is meeting the requirements put forward by the Technical Working Group:
* DVD-ROM drives must read recordable media.
* All DVD media types should be self-identifying.
* Random recording and playback.
* Data integrity of recordable media must be equivalent to that of DVD-ROM.
* Transparent Defect Management.
* Optional cartridge or caddy.
* Low cost.
* Support of copy protection.
DVD-RAM is providing the bridge between business storage requirements and consumer expectations. Soon, DVD-RAM-based home video recorders will be available using 80mm discs. These discs will be compatible with a new breed of DVD Video players and recorders that read 120mm and 80mm discs and, of course, the discs are compatible with most contemporary DVD-ROM and DVD-RAM drives found in state-of-the-art PCs, and this is just the beginning.
Werner Glinka is the principal of the Glinka company which provides technology, marketing, and communications services to the high tech industry. He represents Hitachi on the DVD-Forum U.S. Planning Conference Committee. Hirofumi Sukeda is a senior researcher and the manager of the Optical Disc Storage R&D Center for the Information Storage Research Department of the Central Research Laboratory at Hitachi. He also is the Secretary of the DVD-Forum Working Group 5, which is responsible for DVD-RAM Format development.
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|Title Annotation:||Technology Information|
|Publication:||Computer Technology Review|
|Date:||Aug 1, 2000|
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