Optical disc drive beam on a smaller spot size and to read smaller pits. DVD lens supports a different focus for CD or DVD media with same laser. With the newer Blu-ray disc drives, the laser only has to penetrate 0.1 mm of material. Thus the optical assembly would normally have to have an even greater focus range. In practice, the Blu-ray optical system is separate from the DVD/CD system. During the times of CD writer drives, they are often marked with three different speed ratings. In these cases, the first speed is for write-once (R) operations, the second speed for re-write (RW)
Track (optical disc) a "Sequential Recording Range Information" (SRRI) field of a "Disc Management Area" (DMA). Sessions contain logical tracks, which can be split to create new tracks. A final, "invisible" session holds free space in a single logical track, called the invisible/incomplete track. When a disc is finalized or closed, the latest information in the temporary DMAs such as SRRI is taken and copied into the DMA. Track (optical disc) On an optical disc, a track (CD) or title (DVD) is a subdivision of its content. Specifically, it is a consecutive set of "sectors" (called "timecode frames" on audio tracks) on the