Due to concerns about copying of audio content, some record companies produce music CDs with protections which are designed to prevent copying. These CDs may not play in computers, or may prevent users from copying the tracks. Certain types of copy protection violate the Red Book standard, which means that these CDs technically should not carry the CDDA logo. The music CDs also usually include a note in their packaging indicating that they have copy protection measures in place, to alert consumers to the fact that the CDs may not play in all CD players.
Music CDs are compact discs which include digital audio stored in a format which is designed to work in most players, including stereos and CD drives in computers. Also known as audio CDs, music CDs are usually recorded using the Compact Disc Digital Audio (CDDA) standard, also known as the Red Book format after the color of the binding of the book which lists the specifications for audio CDs. Some manufacturers do not follow this format, which can make their music CDs difficult to play.