PROCESS OF DVD RECORDING




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DVD-R Technology

DVD-R Technology DVD-R is a write-once format, like CD-R, uses a constant linear velocity rotation technique to maximize the storage density on the disc surface. Recording begins at the inner radius and ends at the outer. Rotation of the disc therefore varies from 1,648 RPM to 648, depending on a record/playback head's position over the surface.

Recording on DVD-R discs is accomplished through the use of a dye polymer recording layer that is permanently transformed by a highly focused red laser beam. This dye polymer substance is spin-coated onto a clear polycarbonate substrate that forms one side of the "body" of a complete disc. The substrate is injection molded, and has a microscopic, "pre-groove" 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. A thin layer of metal is then sputtered onto the recording layer so that a reading laser can be reflected off the disc during playback. A protective layer is then applied to the metal surface, which prepares the side for the bonding process.

The recording action takes place by momentarily exposing the recording layer to a high power (approximately 10 milliwatt) laser beam that is tightly focused onto its surface. As the dye polymer 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 disc. 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 650 nm) onto the surface of the disc. 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.

Recording Process

Blank DVD-R discs are recorded in a special 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 disc as well as controlling the actual recording itself.

All DVD discs, 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 disc.

There are two methods of writing a DVD-R disc: disc-at-once and incremental writing.

Disc-at-once, as its name implies, is the process of writing an entire disc's worth of data at one time. Data must be consistently provided by a host computer at a full 11.08 megabits per second during any recording to avoid buffer underrun errors. The occurrences of underruns can be minimized by the use of a large writing buffer memory in a DVD-R drive. DVD-R disc-at-once writing is performed such that the lead-in, data area and lead-out areas are all written sequentially. This differs from CD-R disc-at-once writing, where the data area is written first, followed by the lead-in and lead out areas.

Incremental writing allows a user to add files directly to a DVD-R disc one recording at a time instead of requiring that all files be accumulated on a hard disk prior to writing as with the disc-at-once method. The minimum recording size must be at least 32 kilobytes, (even if the file to be recorded is smaller) as this is the minimum error correction code (ECC) block size for DVD. Obviously, a disc that is being written to incrementally cannot be considered a complete volume until the final information has been stored or the disc 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 "unfinalized" disc (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 finalization, a disc can then be read by a destination playback device, but can no longer have data added to it.

CD-R Versus DVD-R

The primary advantages of DVD-R drives, are higher capacity and compatibility with all DVD players and drives. To help achieve 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 (n.a.) of the lens that focuses it.

Rewritable DVD

The rewritable DVD's specification is based on input from a wide range of sources, including end users, PC manufacturers, CD- and DVD-ROM drive manufacturers, media manufacturers and software developers. The DVD specification is designed to offer data-storage and distribution markets a smooth migration path from CD to DVD.

As rewritable DVD technology is new, there isn't an unic format yet. Different companies applay diffferent formats. At the moment there are three type of rewritable DVD. These are: DVD-RAM, DVD-RW and DVD-R/W.

Because of this, compatibility is the problem of recordable DVD. To override this problem the DVD+RW group offers a solution for future data-storage requirements, By eliminating the need for a caddy, ensuring CD-R compatibility and offering a slightly higher capacity.

DVD VIDEO

DVD Video is the new way in home entertainment. A single DVD Video disc can hold an entire movie on one side while bringing together the high-quality, digital surround sound of compact discs with crisp, high-resolution video. As a system it consists of a mastering system, a physical distribution medium (the disc itself) and a player

The Players

The players consist of the following major components:

• Disc Reader Mechanism: consists of the motor which spins the disc and the laser which reads the information.
• The DVD-DSP (digital signal processor): an integrated circuit that translates the laser pulses back into electrical form that other parts of the decoder can use.
• The Digital Audio/Video Decoder: This complex integrated circuit reconstitutes the compressed data on the disc, converting it into studio-quality video and CD-quality audio for output to TVs and stereo systems.
• Micro controller: This device controls the operation of the player, translating user inputs from the remote control or front panel into commands for the audio/video decoder and the disc reader mechanism. The micro controller would also be responsible for implementing parental lockout, dialing distributors for access codes and controlling decryption.

DVD Player Architecture