Tech Tip:What Are The Differences Between Disc-At-Once, Track-At-Once, And Session-At-Once (Multisession) Cd-R Writing Modes?
Disc-at-once (DAO) mode writes all of the data to CD at one time, in one continuous pass. No interruptions of the data stream are possible. The lead-in, program data, and lead-out areas are all written in this pass. Additional data can't be added later. Masters for mass production must be written in disc-at-once.
Track-at-once (TAO) mode allows various tracks to be written in multiple passes, although they are burned in the same session. The laser is stopped and restarted, which leaves run-out and run-in blocks between the tracks. Usually these are not noticeable, but certain hardware/software combinations could leave some "junk" in a gap, resulting in slight click. Also, CD mastering plants may not accept track-at-once recorded CDs, because the gaps between tracks might be read as errors. After all of the tracks are written, the lead-in, program data, and lead-out areas are added to enable the disc to be read by a CD or CD-ROM drive.
Session-at-once (SAO) mode, like track-at-once, writes data to the CD in multiple passes. However, the disc can be removed and reinserted into the burner. Each session contains its own lead-in, program data, and lead-out, enabling data to be written onto free space of a CD that has some previously recorded data on it (but not written over the data already on the disc). Not all CD readers can read a multisession disc; audio players can only read the first session. For this reason, if you are making an audio CD, it's safer to make a disc-at-once to be sure that it can be played by anyone.