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)
Picture disc the discs as a medium for propaganda. Adolf Hitler and British fascist Oswald Mosley were each featured on their own special picture discs. Most of these records were made of a simple sheet of fairly thin printed cardboard with a very thin plastic coating and their audio quality was substandard. Some were more sturdy and well-made and they equaled or actually surpassed the audio quality of ordinary records, which were still made of a gritty shellac compound that introduced a lot of background noise. In 1933, RCA Victor in the U.S. issued a few typical cardboard-based picture records but was