The first of the two polycarbonate discs carries the dye layer that is topped by an alloyed silver or gold reflective layer. The other polycarbonate layer is purposed as a "dummy disc" to maintain the mechanical strength and durability of the DVD-R as a whole. The dummy disc also serves to protect the data layers from scratches and other damage.
The sandwiched polycarbonate layers also allow the drive's laser to reach the recording layer in nearly half the laser wavelength of a CD, which therefore allows the beam to write data with more accuracy than some optical storage predecessors.
The pregrooves of the DVD-R have a wobble frequency instead of perfectly spiraled pregrooves. This indicates that the groove wanders at a specific modulated frequency to guarantee precise tracking and timing at a high pit density.