RIVER RIVER DVD-R 4.7Gb 16x

DVD-R is a "write once" technology that can be used in DVD-RW recorders and read by nearly any computer DVD drive or DVD player. DVD-R media uses only cyanine recording dyes which appear violet on the recording side of the disc.

The laser of your DVD-RW drive heats the dye to a temperature of about 200 C, irreversibly melting a pitted pattern into the recording layer. A plastic layer alongside the dye expands into the newly available space creating a pit pattern similar to that of a conventional DVD. Your DVD player reads this highly reflective pattern for playback. Because the plastic layer melts into the dye layer to set the pattern, DVD-R discs cannot be re-recorded.

Unlike a stamped DVD, DVD-Rs are manufactured with a spiral groove (like a phono disc) called the pregroove. It provides a precise track for the writing laser to follow. A DVD player depends on following the recorded track of pits in order to track the spiral path.
River Media Products - Cross section of a CD-R

River Media Products - Cross section of a CD-R

A slight wobble in the pregroove in a pre-established pattern generates a frequency used as a carrier signal; the timing information helps regulate servo motors, tracking of the laser assembly, and focus of the beam. Land pre-pits molded into the substrate provide address information and pre-recorded data, used to initiate write operations.

The larger storage capacity of a DVD-R compared to a CD-R is achieved through a smaller pit size and smaller track pitch of the groove spiral which guides the laser beam. Consequently, more pits can be written on the same physical sized disc. In order to write smaller pits onto the recording dye layer a red laser beam with a wavelength of 650 nm (for general use recordable DVD, versus a wavelength of 780 nm for CD-R) is used in conjunction with a higher numerical aperture lens. Because of this shorter wavelength DVD-Rs use different dyes from CD-R to properly absorb this wavelength.

DVD-R discs are composed of two 0.6 mm polycarbonate discs bonded with an adhesive to each other. One contains the laser guiding groove and is coated with the recording dye and a silver alloy or gold reflector. The other layer is an ungrooved "dummy" disc to assure mechanical stability of the sandwich structure and compatibility with the compact disc standard geometry which requires a total disc thickness of about 1.2 mm.
River Media Products - Cross section of a DVD-R

River Media Products - Cross section of a DVD-R

Two methods are typically used to bond the two substrates together:

Hot-melt method: A thin coat of melted adhesive is spread over each substrate and then the two surfaces are bonded by means of a hydraulic ram.
UV method: A thin layer of lacquer is distributed over the disc surface to be bonded, either by rotating the disc or through silk screening. Ultraviolet light is then applied to harden the lacquer.

The sandwich structure also helps protect the data containing layer from scratches by the thick "dummy" disk. Compared to a CD's 1.2 mm of polycarbonate, a DVD's laser beam only has to penetrate 0.6 mm of plastic in order to reach the dye recording layer, which allows the lens to focus the beam to a smaller spot size to write smaller pits.

DVD-R recording requires a more complex write strategy to establish the appropriate lengths for the pits, which are approximately half the size of those on a CD-R disc. The spacing between the pits and lands within the spiral data pattern is also significantly less than on a CD-R disc.
River Media Products - Comparision of CD and DVD pit size

River Media Products - Comparision of CD and DVD pit size

To compensate for the extra precision required during write operations, the laser pulses are very carefully controlled, both in terms of intensity and duration. During recording, the laser is rapidly modulated between the power setting required for writing and the setting used for reading to avoid overheating the media surface and to regulate the size of the mark seared in the dye. A technique known as Optimum Power Calibration (OPC) is used to perform test write operations to a specified calibration area on the recordable media surface and then to read back the test and adjust the laser power settings to match the recorder to the media. Given the extra precision required for recordable operations using DVD-R, this feature becomes a highly desirable addition to any recorder and helps ensure the most consistent results when performing disc recording.

What Makes River Media DVDRs the professionals best kept secret?

Error correction in DVD media is measured with PI and PO (parity inner and parity outer). Where as in CD error correction C1 errors that are not corrected become C2 errors, in DVD a uncorrected PI error becomes the more severe PO error. River Media DVDs are the culmination of many years of manufacturing and technical excellence. As a result the performance is second to none. Below are results from PI/PO scans of our DVD-R compared to a leading competitor.

River Media Products - Performance comparisons

River Media Products - Performance comparisons

River media printable surfaces

Recording performance has been heavily optimised and improved over the years, as has the printable surfaces. River Media printable disc surfaces feature: