A groove is the spiral-shaped groove in a compact disc( CD) or DVD. The groove contains the pits and lands that represent the stored information.
The groove of a CD-R has a track width of 1.6 µm, a groove width of 0.7 µm at the top and 0.2 µm at the bottom, and a groove depth of 0.200 µm. The side edge of the groove has a slope of 50 degrees. The start and end points of the groove are at 22 mm and 58.1 mm from the CD center. For DVDs and Blu-Ray discs, the groove parameters are correspondingly smaller because these optical storage media use shorter-wavelength lasers. The groove width is 0.7 µm for DVDs and only 0.32 µm for Blu-Ray discs.
One parameter for the groove properties is their reflectivity, the Intensity Groove (IG), which is measured before and after writing to a compact disc at several points on the groove.