Recording in disk-at-once mode writes the complete disc, i.e. lead-in, one or more tracks and lead-out, in a single step. The commonly used track-at-once (TAO) mode writes each track independently which requires link blocks between two tracks. Older CD-recorder models forced a two second pause (pre-gap) between two tracks whereas newer models allow adjusting of the pause length in TAO mode reducing the number of link blocks to a minimal amount. However, with TAO it is generally not possible to define the data that is written in pre-gaps. But exactly this feature makes audio CD recording interesting, e.g. by creating hidden bonus tracks or track intros in pre-gaps like it is common habit on commercial CDs. Finally, DAO recording is the only way to write data to the unused R-W sub-channels for e.g. CD-G or CD-TEXT.