The invention: Anonmagnetic storage medium for computers that can hold much greater quantities of data than similar size magnetic media, such as hard and floppy disks.
The people behind the invention: Klaas Compaan, a Dutch physicist Piet Kramer, head of Philips’ optical research laboratory Lou F. Ottens, director of product development for Philips’ musical equipment division George T. de Kruiff, manager of Philips’ audio-product development department Joop Sinjou, a Philips project leader
Holograms Can Be Copied Inexpensively
Holography is a lensless photographic method that uses laser light to produce three-dimensional images. This is done by splitting a laser beam into two beams. One of the beams is aimed at the object whose image is being reproduced so that the laser light will reflect from the object and strike a photographic plate or film. The second beam of light is reflected from a mirror near the object and also strikes the photographic plate or film. The “interference pattern,” which is simply the pattern created by the differences between the two reflected beams of light, is recorded on the photographic surface. The recording that is made in this way is called a “hologram.” When laser light or white light strikes the hologram, an image is created that appears to be a three-dimensional object.
Early in 1969, Radio Corporation of America (RCA) engineers found a way to copy holograms inexpensively by impressing interference patterns on a nickel sheet that then became a mold from which copies could be made. Klaas Compaan, a Dutch physicist, learned of this method and had the idea that images could be recorded in a similar way and reproduced on a disk the size of a phonograph record. Once the images were on the disk, they could be projected onto a screen in any sequence. Compaan saw the possibilities of such a technology in the fields of training and education.
Computer Data Storage Breakthrough
In 1969, Compaan shared his idea with Piet Kramer, who was the head of Philips’ optical research laboratory. The idea intrigued Kramer. Between 1969 and 1971, Compaan spent much of his time working on the development of a prototype.
By September, 1971, Compaan and Kramer, together with a handful of others, had assembled a prototype that could read a black-and-white video signal from a spinning glass disk. Three months later, they demonstrated it for senior managers at Philips. In July, 1972, a color prototype was demonstrated publicly. After the demonstration, Philips began to consider putting sound, rather than images, on the disks. The main attraction of that idea was that the 12-inch (305-millimeter) disks would hold up to forty-eight hours of music. Very quickly, however, Lou F. Ottens, director of product development for Philips’ musical equipment division, put an end to any talk of a long-playing audio disk.
Ottens had developed the cassette-tape cartridge in the 1960′s. He had plenty of experience with the recording industry, and he had no illusions that the industry would embrace that new medium. He was convinced that the recording companies would consider forty-eight hours of music unmarketable. He also knew that any new medium would have to offer a dramatic improvement over existing vinyl records.
In 1974, only three years after the first microprocessor (the basic element of computers) was invented, designing a digital consumer product—rather than an analog product such as those that were already commonly accepted—was risky. (Digital technology uses numbers to represent information, whereas analog technology represents information by mechanical or physical means.) When George T. de Kruiff became Ottens’s manager of audio-product development in June, 1974, he was amazed that there were no digital circuit specialists in the audio department. De Kruiff recruited new digital engineers, bought computer-aided design tools, and decided that the project should go digital.
Within a few months, Ottens’s engineers had rigged up a digital system. They used an audio signal that was representative of an acoustical wave, sampled it to change it to digital form, and en-
coded it as a series of pulses. On the disk itself, they varied the length of the “dimples” that were used to represent the sound so that the rising and falling edges of the series of pulses corresponded to the dimples’ walls. A helium-neon laser was reflected from the dimples to photodetectors that were connected to a digital-to-analog converter.
In 1978, Philips demonstrated a prototype for Polygram (a West German company) and persuaded Polygram to develop an inexpensive disk material with the appropriate optical qualities. Most important was that the material could not warp. Polygram spent about $150,000 and three months to develop the disk. In addition, it was determined that the gallium-arsenide (GaAs) laser would be used in the project. Sharp Corporation agreed to manufacture a long-life GaAs diode laser to Philips’ specifications.
The optical-system designers wanted to reduce the number of parts in order to decrease manufacturing costs and improve reliability. Therefore, the lenses were simplified and considerable work was devoted to developing an error-correction code. Philips and Sony engineers also worked together to create a standard format. In 1983, Philips made almost 100,000 units of optical disks.
Consequences
In 1983, one of the most successful consumer products of all time was introduced: the optical-disk system. The overwhelming success of optical-disk reproduction led to the growth of a multibillion-dol-lar industry around optical information and laid the groundwork for a whole crop of technologies that promise to revolutionize computer data storage. Common optical-disk products are the compact disc (CD), the compact disc read-only memory (CD-ROM), the write-once, read-many (WORM) erasable disk, and CD-I (interactive CD).
The CD-ROM, the WORM, and the erasable optical disk, all of which are used in computer applications, can hold more than 550 megabytes, from 200 to 800 megabytes, and 650 megabytes of data, respectively.
The CD-ROM is a nonerasable disc that is used to store computer data. After the write-once operation is performed, a WORM becomes a read-only optical disk. An erasable optical disk can be erased and rewritten easily. CD-ROMs, coupled with expert-system technology, are expected to make data retrieval easier. The CD-ROM, the WORM, and the erasable optical disk may replace magnetic hard and floppy disks as computer data storage devices.
See also Bubble memory; Compact disc; Computer chips; Floppy disk; Hard disk; Holography.
