A mode on a CD-R drive which determines how the data is to be written to the disc. Disc at once (DAO) writes all the multi-track data in one session, back to back, without turning off the laser between tracks. This is good for red book CDs, as there is no gap between tracks as created with track at once mode. DAO is good for burning the raw data from a multi-track image. Interestingly, unlike TAO, the disc is fixated before the burning process begins.