Some information about compact disk
Compact disc is a digital optical disc data storage format that was co-developed by Philips and Sony and released in 1982. The format was originally developed to store and play only sound recordings but was later adapted for storage of data.
With support from large corporations, the technology was further improved and enhanced to ensure it was ready for the market. In 1978, Polygram, a division of Philips, chose polycarbonate as the material of choice for the CD. Many other decisions were also made that year, such as the disc diameter (115 mm) and the type of laser to be used by CD players. It was also decided that data on a CD would start at the center and spiral outwards to the edge.
In 1979, a prototype CD system was demonstrated in Europe and Japan; Sony then agreed to join into the collaboration, and both Sony and Philips compromised on the standard sampling rate of 44.1 kHz and the choice to use 16-bit audio. The disc diameter was changed from 115 to 120 mm to allow for 74 minutes of playback with the sampling rate and quality chosen.
The compact disc first surfaced in the public eye 15 years after its invention when Philips made an announcement on May 17, 1978. The new standard was proposed by Philips and Sony in 1980 as “Red Book”, which was a set of color-bound books containing the technical specifications for all CD and CD-ROM formats. The standard is not free, and a license (known as an IEC 60908 document) must be obtained from Philips for US$210 as a PDF. In 1981, Matsushita accepted the new CD standard, but the collaboration between Sony and Philips ended as the two companies had products ready for 1982.
CDs are made from 1.2 mm thick polycarbonate plastic weighing about 16 grams. A thin layer of aluminum is applied to the surface, making it reflective, and then protected by a film of lacquer. The most common printing method for compact discs is screen-printing.
The data on a CD is stored as tiny indentations encoded in a spiral track moulded into the top layer of polycarbonate. Digital data on a CD begins at the center and proceeds outwards to the edge, allowing for flexibility as many different sizes of CDs can be made; the most common being 12 cm in diameter (known as maxi singles when used for storing music). A CD is read using a semiconductor laser that focuses through the bottom of the polycarbonate layer.