EVOLUTION OF OPTICAL MEDIA
Compact Disc (CD-ROM, CD-Audio, CD-Video)
Released in 1982, the CD (compact disc) revolutionized the music and movie industry by offering digital sound/film to home consumers in replacement of analog formats (VHS). In 1990, the CD-R, a variant of CD was introduced as a storage media which could be used with personal computers. 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.
Besides CD-R, CD also has some other formats like CD-RW with the same 700MB storage capacity. While CD-R allows the user to write information on it only once, CD-RW allows information to be written and erased as long as the disc surface is still in good condition.
Digital Versatile/Video Disc (DVD-ROM, DVD-Audio, DVD-Video)
Released in the late 1990s, DVDs offer 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. It could also be used for audio files called DVD-Audio which is uncompressed studio master recordings that offer much higher bit-rate than a standard CD. DVDs use a red wavelength laser, much like CDs.
DVD also has some other formats like DVD-R and DVD-RW with the same storage capacity of 4.7 GB storage. With DVD-R, information can be written only once while with DVD-RW you can write, erase and rewrite as many times as possible or as long as the surface of the disc is still in good condition.
High Definition DVD
HD-DVD was released by Toshiba as a higher format than DVD both in size and in visual quality. HD-DVD offered enough storage space for full-length, high-definition movies on a single disc. HD-DVD discs are 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 to Blue-Ray discs, 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 more 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 was one of the first optical media. A laser disc was a 12-inch disc that held a digital copy of a movie. Laser discs are not efficient at storage Because of low size. It takes multiple discs for a full-length movie. Other proprietary, short-lived formats included the GD-Rom from Sega's Dream Cast gaming system, Sony's Mini Disc and Super Audio-CD.
TRANSERVE DISC (C)
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