Pits are the indentations burned into the surface of the compact disc( CD) or DVD by the laser beam, which cause a change in the beam reflection during reading.
For compact discs, pits have a width of 0.5 µm and a length of between 0.83 µm and 3.05 µm. For DVDs, the minimum pit length is 0.40 µm and the maximum is 1.86 µm. For DVD, the pit width is 0.3 µm, and the pit depth is 0.16 µm.
The transition between pits and lands forms the encoded signal information. Since a pit or land must be at least two states long, 16 states are needed to represent one byte.