Что в обозначении DVD-R, DVD+R значат плюсы и минусы?

Vot 4to ja nadibal v nete:

DVDs and CDs have their data encoded on a single spiral which covers the surface of the disc. In case the optical medium is recordable, this spiral contains a slight sinusoidal deviation from a perfect spiral. This deviation is used to encode addressing information. The period of this sine curve corresponds to the wobble frequency. DVD-R has a constant wobble frequency, and DVD+R uses frequency modulation similar to that used by CD-R/RW. DVD+RW has a constant wobble frequency, but encodes its addressing information using phase-modulated wobble addressing.