The compact disc, which originated as a digital audio storage medium, emerged from a joint Sony/Philips project and was first reached the market in 1982. The format stores digital data in the form of pits molded into the top of a plastic disc that has a reflective backing. A laser reads the pits. Because CDs are digital, they are perfect for storing computer data, and it wasn't long before Sony/Philips adapted the format to create computer CD-ROMs, producing the first commercial CD-ROM drive in 1985.
The 12cm optical disc has undergone further development during the past 25 years, resulting in higher-capacity discs such as DVD, HD-DVD, and Blu-ray. More significant was the introduction in 1988 of the CD-Recordable (CD-R), which let users write their own data to the disc. In the late 1990s, as optical media got cheaper, this form of storage supplanted floppies in handling most day-to-day data transfers.
Photos: Benj Edwards/Sony