CD Track at once, as the name implies, records just a single track, and then writes a run-out sequence on the disk. Before the next track is written, a run in sequence of 2 blocks is written. These run-in ( of one link block and 4 further blocks) and run-out sectors are ignored by disk readers, but occasionally can be heard as a click by an audio player.
When writing, the laser is turned off between tracks. Upto 99 tracks may be written on any CD