Track-at-Once recording is what most recorders and software support today. Each time the writing of a track (data or audio) is completed, the recording laser is stopped; each time the laser is stopped it writes Run-Out blocks. When starting again it writes Run-In blocks (a total of 7 blocks). These are ignored by CD-ROM readers and so do not disturb data transmission, but in some audio players you might hear a click between tracks. This is why Disc-at-Once recording is preferable for audio discs.