Digital storage media can be broken into three separate categories--magnetic, flash and optical. Optical storage has been a popular form of storage media due to its low cost, ease in manufacturing and portable size. Optical storage media is generally available on a standard size disc measuring 12cm in diameter. Since 1982, optical media is still the standard for purchased music and movie physical media. Several types of optical media are still in use today.
Released in 1982, the CD (compact disc) revolutionised the music industry by offering digital sound to home consumers in replacement of analogue formats. The CD was eventually transitioned from a music source to a form of storage for data. In 1990, the CD-R was introduced and allowed for the creation of optical discs at home with a personal computer. The average CD allows for up to 700 MB of data storage. Digital bits are stored as pits on the reflective material in the disc. A red wavelength laser detects these pits and converts them to a digital signal.
Digital Versatile/Video Disc
Released in the late 1990s, DVDs offered a widely accepted digital movie format. Allowing 4.7 GB for a single-layer disc and up to 8.5 GB for a dual-layer disc, DVD was an excellent choice for personal backups of data on a DVD-R or movie media. DVD is not only used for data and video. DVD-Audio discs are uncompressed studio master recordings that offer much higher bit-rate than a standard CD. DVDs used a red wavelength laser, much like CDs.
High Definition DVD
HD-DVD was released by Toshiba as a competing format to Sony's Blu-ray disc. HD-DVD offered enough storage space for full-length, high-definition movies on a single disc. HD-DVD discs were capable of holding 15 GB per layer with a maximum of two layers. Toshiba had planned on eventually releasing three-layer discs; however, with shifts of movie production studios, support for HD-DVD dwindled until Toshiba announced it would no longer continue the format. HD-DVD drives use a blue wavelength laser that is able to read smaller pits on the optical media.
Blu-ray is the newest high-definition optical format. Developed by Sony, Blu-ray discs offer 25 GB per layer with up to two layers per disc. Blu-ray discs have a protective coating that reduces the number of scratches and makes the disc durable. Like HD-DVD, Blu-ray offers a full-length, high-definition movie on one disc. Blu-ray recordable, or BD-R, drives are becoming more common in home computers. The BD-R drives allow for up to 50 GB of storage on one disc. Blu-ray drives use the same type of laser as HD-DVD drives to allow for greater storage on the optical disc.
Legacy Optical Devices
There have been a number of optical media that are no longer in production. Laser discs were one of the first optical media. A laser disc was a 12-inch disc that held a digital copy of a movie. Laser discs were not efficient at storage; it often took multiple discs for a full-length movie. Other proprietary, short-lived formats included the GD-Rom from Sega's DreamCast gaming system, Sony's MiniDisc and SuperAudio-CD.