Use blue laser, which has a shorter wavelength than the red laser used by CDs, allowing it to focus on the tinier tracks of the DVD.
Use multiple layers of tracks
Blue laser beams can penetrate the plastic and focus at different depths
Some are dual-layered- two sets of tracks on one side of the disk, one beneath the other. This doubles the capacity of one side of a DVD disk.
A double layer double side (DLDS) DVD drive uses double layers and can read double-sided disks, giving it four times the capacity of a single layer single side (SLSS) drive.