{"id":30317,"date":"2019-10-31T21:34:50","date_gmt":"2019-10-31T18:34:50","guid":{"rendered":"https:\/\/prohoster.info\/blog\/kak-vse-nachinalos-opticheskie-diski-i-ih-istoriya\/"},"modified":"2019-10-31T21:34:50","modified_gmt":"2019-10-31T18:34:50","slug":"kak-vse-nachinalos-opticheskie-diski-i-ih-istoriya","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/kak-vse-nachinalos-opticheskie-diski-i-ih-istoriya","title":{"rendered":"How it all began: optical discs and their history","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

\"How
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\nOptical compact discs became publicly available in 1982, but the prototype was introduced even earlier \u2014 in 1979. Initially, CDs were developed as a replacement for vinyl records, offering a higher quality and more reliable storage medium. It is believed that laser discs are the result of a collaboration between two technology corporations \u2014 Japan's Sony and the Netherlands' Philips.<\/p>\n

The fundamental technology of 'cold lasers', which made the advent of laser discs possible, was developed by Soviet scientists. Alexander Prokhorov<\/a><\/noindex> and Nikolay Basov<\/a><\/noindex>. For their invention, they were awarded the Nobel Prize. Over time, the technology evolved, and in the 1970s, Philips developed a method for recording compact discs, which laid the groundwork for the CD. Initially, the company's engineers created ALP (audio long play) as an alternative to vinyl records.
\n <\/a><\/noindex>
\nThe diameter of ALP discs was approximately 30 centimeters. Shortly thereafter, engineers reduced the diameter of the discs, decreasing the playback time to 1 hour. Laser discs and the playback device for them were first demonstrated<\/a><\/noindex> by Philips in 1979. Following this, the company sought a partner for further development of the project \u2014 the technology was envisioned by its developers as international, and it was challenging to advance it to the necessary level and promote it independently.<\/p>\n

The Beginning of It All<\/h3>\n

\nManagement decided to try to establish contacts with technology companies from Japan, which at that time was at the forefront of hi-end technologies. To this end, delegates from Philips were sent to the country, and they managed to meet with the president of Sony, who was interested in the technology. <\/p>\n

Almost immediately, there was formed<\/a><\/noindex> The team of engineers from Philips-Sony developed the first specifications for the technology. The vice president of Sony insisted on increasing the disc capacity; he wanted it to hold Beethoven's Ninth Symphony, which is why the disc's capacity was expanded from 1 hour to 74 minutes (there's also an opinion that this is just a nice marketing story). The amount of data that fits on such a disc is 640 MB. The engineers also developed the audio quality parameters. For instance, the sampling frequency of stereo signals was regulated at 44.1 kHz (22.05 kHz for a single channel) with a bit depth of 16 bits each. Thus, the Red Book standard was born.<\/p>\n

The name of the new technology did not appear out of nowhere \u2014 it was chosen from several options, including Minirack, Mini Disc, and Compact Rack. Ultimately, the developers combined two names to arrive at the hybrid term Compact Disc. This name was partly chosen due to the growing popularity of audio cassettes (the technology Compact Cassette<\/a><\/noindex>).<\/p>\n

Philips and Sony also played a crucial role in developing the specifications for the first digital compact discs, which were named Yellow Book or CD-ROM. The new specification made it possible to store not only audio but also text and graphic data on discs. The type of disc was identified automatically when reading the header. The problem was that a compact disc that complied with the Yellow Book standard could only work with a specific type of drives that were not universal.<\/p>\n

On August 17, 1982, the first CD was released at the Philips factory in the German town of Langenhagen. It contained the album The Visitors<\/a><\/noindex> by the group ABBA. It's worth noting that the lacquer coating on the first discs was not very high quality, so buyers often damaged the compact discs. Over time, the quality of discs improved. For the first few years, they were used exclusively in hi-fi equipment, serving as a replacement for vinyl records and cassettes.<\/p>\n

\"How
\n
\nSince 2000, 700 MB disks have become available for sale, allowing audio recordings with a total duration of up to 80 minutes. They have completely replaced the 650 MB disks in the market. There are also 800 MB media, but these were not compatible with all drives, so they did not gain significant popularity. The increase in available storage capacity was achieved by reducing the distance between the tracks. For example, the distance between tracks on 650 MB disks is 1.7 \u00b5m, while for 800 MB disks, this figure is reduced to 1.5 \u00b5m. Additionally, the speed of the former is 1.41 m\/s, while for the latter, it is 1.39 m\/s.<\/p>\n

\"How
\n <\/p>\n

How it works<\/h3>\n

\nThe disk consists of several layers. The substrate is polycarbonate, with a thickness of 1.2 mm and a diameter of 120 mm. Another layer, metal (which can be gold, silver, or, most commonly, aluminum), is placed on the substrate. The metal layer is then protected by varnish, onto which graphics are applied. The substrate reliably protects the metal layer, so very deep scratches hinder reading. The diameter of the hole in the disk is 15 mm.<\/p>\n

The storage format for disks is Red Book<\/a><\/noindex> (as mentioned above). Errors during reading are corrected using Reed-Solomon code, so light scratches do not reduce the readability of the disk.<\/p>\n

Data is written to the disk in the form of a spiral track made up of so-called pits (depressions), which are pressed into the polycarbonate base. The depth of each pit is approximately 100 nm, while the width is 500 nm. The length of a pit ranges from 850 nm to 3.5 \u00b5m. Pits scatter or absorb light, while the substrate reflects it. Thus, a recorded disk is an excellent example of a reflective diffraction grating.<\/p>\n

The disk is read using a laser beam with a wavelength of 780 nm, emitted by a semiconductor laser. The reading principle is based on detecting changes in the intensity of reflected light. The laser beam focuses on the information layer, with a light spot diameter of 1.2 \u00b5m in this case. The maximum signal is recorded between the pits. When the laser hits a pit, a lower light intensity is recorded. Changes in intensity are converted into an electrical signal, which the equipment then processes.<\/p>\n

How a disk is created<\/h3>\n

<\/p>\n