CD player in 1970. Following litigation, Sony and Philips licensed Russell's patents (then held by a Canadian company, Optical Recording Corp.) in the 1980s. The Compact Disc is an evolution of LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals. Prototypes were developed by Philips and Sony independently in the late 1970s. In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the "Red Book" CD-DA standard was published in 1980. After their
CD-R the cost of typical recorders was down to $10,000–12,000, and in September 1995, Hewlett-Packard introduced its model 4020i manufactured by Philips, which, at $995, was the first recorder to cost less than $1000. The dye materials developed by Taiyo Yuden made it possible for CD-R discs to be compatible with Audio CD and CD-ROM discs. Initially, in the United States, there was a market separation between "music" CD-Rs and "data" CD-Rs, the former being several times more expensive than the latter due to industry copyright arrangements with the RIAA. Physically, there is no difference between the discs save for the