CD-Extra is a Blue Book standard recording format. It was previously called CD-Plus and CD-Enhanced (Enhanced CD). This format has none of the disadvantages of standard mixed mode CDs. On mixed mode CDs the first track always contains an ISO file system, which means that audio CD players cannot play the first track of this type of CD. In contrast, CD-Extra has two sessions.
The first session contains up to 98 audio tracks conforming to the Red Book standard. The second session contains the ISO track with the ISO9660 file system and the directories CDPLUS and PICTURES. This means that CDs in CD-Extra format can be played on both CD drives and audio CD players, as the second session cannot be "seen" by the audio CD player.