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 from the late 1940s through the 1950s. Their most popular and well-known issues resembled Vogue records in their general style of illustration and use of high-quality materials, but they were only 7 inches in diameter, had no reinforcing core disc, and sold for a much lower price. Other companies such as Voco also made picture discs for children. Red Raven Movie Records, introduced in 1956, were a very unusual type of children's picture disc. They featured a sequence of sixteen interwoven animation frames arrayed around the center and were to be played at 78 rpm on a turntable with a