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 many years later. These were deluxe picture discs, priced much higher than ordinary records, and they sold in very small numbers. In the early 1930s the entire record industry was being devastated by a worldwide economic depression and the proliferation of the new medium of radio, which made a wide variety of music available free of charge. Picture discs of all kinds were among the casualties. With the Great Depression and World War II no longer around to interfere with such modest luxuries, the picture disc reemerged in 1946, when Tom Saffardy's Sav-Way Industries began issuing Vogue Records. Vogues were