CD-ROM

A CD-ROM (Compact Disk Read Only Memory) is a drive that reads aluminum-coated round plastic discs but is incapable writing to any disc. Invented in the United States on 1972, the CD-ROM standard was officially introduced in 1982 when Philips and Sony agreed on the 4.72-inch size format we now use today.

Later, as Phillips and Sony continued cooperation in the 1980s, additional specifications were announced concerning the use of CD technology for computer data which evolved into computer CD-ROM drives used today.
The CD-ROM diskettes are 12 x 12 cm with a width of .1cm, as shown in the above picture. The disc is made of a polycarbonate wafer and is coated with a metallic film, usually an aluminum alloy. This aluminum film is the portion of the disc that the CD-ROM drive reads for information. The aluminum film (strata) is then covered by a plastic polycarbonate coating that protects the underlying data. A label will usually be placed on the top of the disc and data is read from the bottom of the CD.