#1 Burning Software

There are two basic ways of writing to a CD-R. Disc-at-once (DAO) writes the entire CD in one pass, possibly writing multiple tracks. The entire burn must complete without interruption, and no further information may be added.

Track-at-once (TAO) allows the writes to be done in multiple passes. There is a minimum track length of 300 blocks (600K for typical data CDs), and a maximum of 99 tracks per disc, as well as a slight additional overhead associated with stopping and restarting the laser.

Because the laser is turned off and on for every track, the recorder leaves a couple of blocks between tracks, called run-out and run-in blocks. If done correctly, the blocks will be silent and usually unnoticeable. CDs with tracks that run together will have a barely noticeable "hiccup". Some combinations of software and hardware may leave junk in the gap, resulting in a slight but annoying click between tracks. Some drives and/or software packages may not let you control the size of the gap between audio tracks when recording in track-at-once mode, leaving you with 2-second gaps even if the original didn't have them.

Many recorders, starting with the venerable Philips CDD2000, allow "session-at-once" (SAO) recording. This gives you disc-at-once control over the gaps between tracks, but allows you to leave the disc open. This can be handy when writing CD Extra discs (see section (3-14)).

There are some cases where disc-at-once recording is required. For example, it may be difficult or impossible to make identical backup copies of some kinds of discs without using disc-at-once mode (e.g. copy-protected PC games). Also, some CD mastering plants may not accept discs recorded in track-at-once mode, because the gaps between tracks will show up as uncorrectable errors.

The bottom line is that disc-at-once recording gives you more control over disc creation, especially for audio CDs, but isn't always appropriate or necessary. It's a good idea to get a recorder that supports both disc-at-once and track-at-once recording.

If you use disc-at-once (DAO) recording, the lead-in is written at the very start of the process, because the contents of the TOC are known ahead of time. With most recorders there is no way to specify that more than one session should be created in DAO mode, so creating a multisession disc with DAO recording isn't generally possible. Such discs must be created with track-at-once (TAO) or session-at-once (SAO) recording.