Session, single session, multi session
Session is the unit of CD recording which includes lead in sector, program sector and lead out sector. Each sector has its own directory file that contains the introduction to the format of the current session. The directory file in multi session will include the introduction to the format of the sector before.
Single session is the common burning method, this method can save space. Compact disc is usually single session disc.
Multi session disc refers to disk with two or more than two sessions. This type of burning method is very convenient. The disk can be burned again if the CD-R has enough space. But the multi session burning requires a 30MB space interval between each session. Thus, multi session usually wastes space of disc. Compact disc with-CD Extra format is the disc with two sessions.
This area is at the beginning of the session that is used to store data on the disc size, starting position of each Optical track, Optical track length and so on. The lead in area of each sector would be 1 minute long.
The lead out area usually comes at the end of each session that indicates the end, readable session or the length of the entire disc. The lead out area of the first session on the disc is 1.5 minutes long and the lead out area in other session is 30 second long.