The polycarbonate layer of a CR-R or CD-RW has a spiral pre-groove that is formed when the disc substrate is injection molded against a stamper.
The read/write laser in the drive will follow this pre-groove track as it is writing, in order to maintain the spacing between the written tracks with a high degree of accuracy.
This spiral has a wobble frequency introduced into it, which the drive can read while it is writing. The drive will synchronize the rotation speed to the reference speed of the wobble signal, allowing it to maintain an accurate linear velocity (the speed of the track as it passes the laser). This wobble is further modulated with a timecode reference signal containing minutes, seconds and frames. This modulated signal is known as ATIP