DAO and TAO

[GrfxArt]

Concerning CD/DVD burning, what is the difference between DAO (Disc-at-once) and TAO (Track-at once)? Please give examples of when you'd select those options. ThanksIA

[Miz]

With standard recording modes such as DAO & TAO, the recorder adds all the extra information such as forward error correction, CRC checksums, etc. while recording to the CD.

DAO/96 writing sets the CD recorder to raw writing and leaves it up to the recording software to add all the extra error checking information and CRC information to the data as it's being written to the CD. DAO/96 is also used by Clone CD, Blindwrite, etc. to copy some protected CDs as the software can replicate bad sectors (often used as copy protection) by simply putting in invalid CRC checksums while writing the sectors to mark as bad.

I'm not quite sure why the very end of a TAO session is unreadble, but I think it's due to the CD Recorder turning off the laser at the end of a session to prepare for the lead in/out. Either that or Nero's surface scan tries reading too many sectors and goes a little ahead of the end of the session.

With DAO, the laser stays on throughout the entire disc, this means that there is no loss in recording time between when it records the session and the lead in/out tracks. In DAO, it starts with the leadin, then the track and finally the leadout without switching off the laser the whole way through. With SAO, it starts writing the track, moves the laser back to the center of the disc and starts writing the lead in and lead out.

The advantage of multisession use to be useful back in the early days of CD recording for archival purposes. With multisession, you can write a session to a CD and at a later stage, add another session to a CD and so on until the capacity of the CD has reached. When you add another session to a CD using Nero for example, it will show you in the left panel what's already on the CD in a different shade of colour than you drag into that column. This way you can tell what's already on the CD and about to add. When a second or further session is added, another track is written to the CD. A marker is then added to the previous table of contents to mark that there is a new session on the CD. The marker points to the new table of contents. Another lead in/lead out is also written. This extra overhead takes about 30MB, so when adding sessions to a CD, I'd recommend a reasonable session size such as 100MB or more. Multisession CDs can be read by just about every CD-ROM drive out there from the days of 8x onwards. Once CD-RWs bacame popular, multisession CD-Rs died.
(Source)

I'm not so sure about that last sentence. I use multi-session CD-Rs exclusively since CD-RWs are not all that reliable as far as being able to retrieve the data on any and every CD drive.

[reboot]

DAO for full disks, iso, movies, generally everything on a CDR.
TAO for multisession. eg a CDR to which you add data, then later add a small video, later still more data, until it's full.
DAO "closes" the disk so no more can be written to it.
TAO allows you to add.
TAO is very rarely used, and confuses people to no end when writing audio disks. Because each song is a "track" they feel they must write the disk in TAO, which is totally wrong.

[GrfxArt]

Oh okay that might explain why a movie I'm playing on my DVD player will freeze up, I've had the burn software on the TAO setting. I burned the same movie with DAO and it seems to be smoother and didn't freeze. Thanks again

[reboot]

That would explain it allright

[Nuclear Krusader]

Originally posted by Miz I'm not so sure about that last sentence. I use multi-session CD-Rs exclusively since CD-RWs are not all that reliable as far as being able to retrieve the data on any and every CD drive.

Ditto. I use multisession CD-Rs since my MP3 portable player canna read CD-RWs.

[RayH]

As far as I know, from my days with a 4x burner, TAO made coasters and DAO made playable CD's!