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
Green Book (CD standard) on CD-i tracks, as well as certain specific files that are required to be present in a CD-i compatible disc. The CD-i Ready format is a type of bridge format, also designed by Philips, that defines discs compatible with CD Digital audio players and CD-i players. This format puts CD-i software and data into the pregap of Track 1. The CD-i Bridge format, defined in Philips' White Book, is a transitional format allowing bridge discs to be played both on CD-ROM drives and on CD-i players. Green Book (CD standard) The "Green Book", formally known as the "CD-i Full Functional