1=A Compact Disc (also known as a CD) is an optical disc used to store digital data. It was originally developed to store sound recordings exclusively, but later it also allowed the preservation of other types of data. Audio CDs have been commercially available since October 1982. ...

2=The compact disc and more specifically, audio compact disc (CD-DA) were introduced in the market in 1980 by Philips and Sony as an alternative to the vinyl disc and audio cassettes.

In 1984 both companies extended the technology so it can be used to store and retrieve data an so the CD-ROM was born. Since then, the compact disc has change significantly the way we listen music and store data.

This disc has 650 Mb capacity for data or 74 minutes for high quality audio. In a wide manner, we can say that compact disc has change dramatically the way music is distributed today and, more widely, the way electronic information is distributed.

In 1990 again Philips and Sony expand the technology and created the Recordable compact disc (CD-R). Up to then, the CDs were manufactured by industrial stamping with a master made from the original.

The disc is then spread with a thin aluminium layer which gives the cd silver aspect. Today this technology is used for quantities larger than 500 units, while for smaller quantities it is cheaper and faster to replicate CDr.

The recording layer it is also quite characteristic. Originally, this was a gold derivative and disc had such colour. Today other cheaper and longer lasting compounds are used.

Today, after 14 year since Sony and Philips started the digital entertainment revolution, a new product has been introduced: the DVD. None of the original derivatives (CD-rom, Photo-CD, CD-i, etc) create such expectations ad DVD, not only for the large capacities DVD have, but also the significant advances in software development, specially compression algorithms for video applications.

In 1995 it was when Sony led a 9 company consortium to introduce a standard for recordable DVD. Today, though, the DVD-r is not standardized and to types of systems coexists: DVD-R and DVD+R.