CD-RW

The idea of storing information on an optical disc dates back to the 1950s. Americans such as David Paul Gregg and James Russell envisioned writing with electron beams and reading with laser beams. The principle of the rotating disc and a reflective surface transformed these intuitions into concrete possibilities.

Around 1970, Hollywood became interested in optical discs for distributing films. MCA and Philips joined forces and launched the first consumer laser videodisc, LaserVision, in late 1978. Helium-neon lasers read the molded pits on a 30 cm disc, whose size recalled that of vinyl records. The video information was encoded in the variable spacing between the edges of these pits, arranged in a spiral.

In 1974, Philips laboratories embarked on developing an optical disc audio system. Their engineers relied on existing technologies while betting on future advances in integrated circuits and semiconductor lasers. The project gained momentum, and the team concluded that digital technology would surpass analog recording. The scale of the undertaking prompted Philips to seek a partner: Sony joined the venture in 1979.

The compact disc adopted a diameter of 120 mm, much more compact than LaserVision. The designers knew that contemporary semiconductor lasers delivered approximately 1 mW at 800 nm. They adjusted the optics accordingly. The laser beam passes through a transparent substrate of 1.2 mm before reaching the data engraved on the aluminum layer of the disc.

The first audio CD players arrived in stores in 1982. The technology found its place in the computing world. Philips and Sony announced the CD-ROM in 1984, and the first drives were delivered the following year as peripherals for large systems. International organizations validated the standard in 1985. However, data organization remained proprietary until 1988, when ISO 9660 became the reference.

Research on recordable and rewritable discs accelerated in the 1970s in the United States, Europe, and Japan. The limited power of lasers hindered progress. In France, Thomson-CSF and later Alcatel Thomson Gigadisc experimented with glass discs coated with layers containing malleable gold. Writing created microscopic bumps, but repeated laser readings deformed these features.

Another approach proved more fruitful for WORM (Write Once Read Many) media: coating glass or plastic with polymer dye mixtures. The optics were those of read-only discs, provided peak power of 50 to 100 mW was available. Philips and Sony defined the recordable CD (CD-R) in their 1988 “Orange Book”. By the late 1990s, the required lasers became affordable and CD-R burning spread throughout personal computing.

Two technologies competed for the rewritable disc market: magneto-optical recording and phase change. The former got off to a strong start in the early 1970s. It relied on synchronizing laser heating with magnetic field modulation. Read/write heads were complex, but the media tolerated a virtually unlimited number of cycles.

Phase-change media use a thin layer of chalcogenide alloy, such as AgInSbTe or GeSbTe. This layer is stable in two states: amorphous and microcrystalline, each exhibiting distinct reflectivity. A brief, intense laser pulse melts the layer, which cools in an amorphous state. A longer but less energetic pulse heats the film without melting it, triggering crystallization. From the 1970s to the 1990s, research refined alloy compositions and deposition processes.

In the mid-1990s, Korean and Taiwanese manufacturers entered the market. The first CD-ROM production in Taiwan and Korea began in 1994. Two years later, Taiwanese manufacturers accounted for 12% of global production. In 1996, LG alone represented nearly 10% of worldwide sales. This competition drove down drive prices.

The number of optical drive manufacturers rose from 2 in 1983 to 16 in 1985, climbed to 65 around 1995, then dropped back to 44 in 1999. Newly created specialized companies initially stimulated technical progress. Before 1988, the year of ISO 9660, the fastest drives relied on proprietary formats. After standardization, electronics and computing giants dominated the performance race.

Prices for optical burners plummeted: $15,000 in 1991, $5,000 in 1993, and under $1,000 in 1995. CD-RW established itself firmly in the computing landscape until the arrival of rewritable DVD in the 2000s. The technology left its mark on the history of digital storage.