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)
History of optical storage media History of optical storage media Although research into optical data storage has been ongoing for many decades, the first popular system was the Compact Disc, introduced in 1982, adapted from audio (CD-DA) to data storage (the CD-ROM format) with the 1985 "Yellow Book", and re-adapted as the first mass market optical storage medium with CD-R and CD-RW in 1988. Compact Disc is still the "de facto" standard for audio recordings, although its place for other multimedia recordings and optical data storage has largely been superseded by DVD. DVD (initially an initialism abbreviation of "Digital Video Disc," then modified to "Digital