In wodim one can choose between many different writing modes like Disk At Once("-dao"), Session At Once("-sao"), Track At Once("-tao") or Raw writing mode("-raw"). As I understand, Track At Once writes one track at time while in SAO and DAO modes laser does not stop between tracks. Is this important only in case of audio CD's and there is no difference in case of data CD's(for example burning Linux distribution image)? In addition, even in case of audio CD's and TAO mode, how does wodim know where one track starts or ends? Am I correct that SAO mode allows one to write multiple times to a CD-R media? Last but not least, in which case is raw writing mode useful?
The CD-DA, CD-ROM, CD-R and CD-RW formats all store information in 2,352 byte sectors, divided into 98 distinct 24-byte frames. On CD-DA discs, each 24-byte frame holds two 16-byte audio samples, one for each stereo channel. The CD-ROM specification defines two sector modes, Mode 1 and Mode 2, which describe two different sector layouts. Both modes reserve the first 16 bytes for header information. Mode 1 uses an additional 288 bytes for error detection (32-bit CRC) and correction (276-byte RSPC).
The notion of sessions was added to the CD format specifications simultaniously with the specifications for the CD-R and CD-RW formats.
Each session consists of three areas that mimic the original structure of CD-DAs and CD-ROMs: the lead-in area contains the sessions Table Of Contents (TOC); the program area holds the individual tracks; the lead-out area marks the end of the session. Although the notion of sessions did not exist at the time the original CD-DA and CD-ROM specifications were written, these older formats consist of what essentially amounts to a single session per disc.
Some disc formats, such as CD-Rs and CD-RWs support multiple sessions per disc. Each session contains one or more tracks. In multi-session discs the TOC in the lead-in area of subsequent sessions includes the addresses of earlier sessions. The TOC in the lead-in area of the latest session is used to access the tracks on the disc.
The ISO 9660 Compact Disc File System (CDFS) standard records an index of files present on a disc in a series of volume descriptors that are stored at a fixed offset from the start of the disc. In contrast, multi-session discs store the volume descriptors at a fixed offset in the latest session. When files are added to a multi-session data disc, an updated copy of the entire directory tree is stored as part of the new session. Files can be "deleted" by removing the reference to the file from the latest session. However, as the actual file data is never altered, "deleted" files can be accessed via the directory tree from a previous session.
There are several recording modes, including the ones explicitly mentioned in the question: