Double-layered writable media have: a first polycarbonate layer with a (shallow) groove, a first data layer, a semi-reflective layer, a second (spacer) polycarbonate layer with another (deep) groove, and a second data layer. The first groove spiral usually starts on the inner edge and extends outerwards, while the second groove Cassette to CD Recorder starts on the outer edge and extends inwards.

There are mechanical limits to how quickly a disc can be spun. Beyond a certain comparison of rotation, around 10000 RPM, centrifugal stress can cause the disc plastic to creep and possibly shatter. On the outer berm of the CD disc, 10000 RPM limitation roughly equals to 52x speed, but on the inner end only to 20x.