The most important part of an optical disc drive is an optical path, placed in a pickup head (PUH), habitually consisting of semiconductor laser, a lense for guiding the laser beam, and photodiodes detecting Cassette to CD the light reflection from disc's surface.
Because keeping a constant transfer relative for the whole disc is not so important in most contemporary CD uses, to keep the rotational speed of the disc safely low while maximizing data rate, a pure CLV approach needed to be abandoned. Some drives work in partial CLV (PCLV) scheme, by switching from CLV to CAV only when a rotational limit is reached.