All You Need to Know About CD (Compact Disc)
A compact disc (popularly known as CD or cedé, for the acronym in English compact disc according to abbreviationfinder) is an optical digital medium used to store any type of information (audio, images, video, documents and other data).
Today, it remains the preferred physical medium for audio distribution.
CD in Spanish language
In Spanish or Castilian you can already write «cedé» (how it is pronounced) because it has been accepted and lexicalized by use; In much of Latin America it is pronounced [sidí], as in English, but the Pan-Hispanic Dictionary of Doubts (of the Association of Academies of the Spanish Language) advises against this pronunciation. The anti- etymological «cederrón» (which comes from the acronym CD-ROM: compact disc-read only memory: ‘ compact disc-read-only memory ‘) is also accepted.
The compact disc was created in 1979 by the Japanese Toshitada Doi (from the Sony company) and the Dutch Kees Immink (from the Philipscompany). The following year, Sony and Philips, which had developed the Compact Disc digital audio system, began distributing compact discs, but sales were unsuccessful due to the economic slump at the time. So they decided to embrace the higher quality classical music market. The launch of the new and revolutionary audio recording format began, which would later be extended to other sectors of data recording.
The optical system was developed by Philips while the Digital Reading and Coding was carried out by Sony, it was presented in June 1980 to the industry and 40 companies from all over the world joined the new product by obtaining the corresponding licenses for the production of players and records. In 1981, the conductor Herbert von Karajan, convinced of the value of compact discs, promoted them during the Salzburg festival (Austria) and from that moment their success began. The first titles to be recorded on compact discs in Europe were the Alpine Symphony (by Richard Strauss), the waltzes by Frederic Chopin (performed by Chilean pianist Claudio Arrau) and the album The Visitors (by Swedish pop group ABBA).
In 1983, the American company CBS (which today belongs to the Japanese Sony Music) released the first compact disc in the United States: an album by pop singer Billy Joel.
The production of compact discs was centralized for several years in the United States and Germany from where they were distributed throughout the world. In the nineties, factories were set up in various countries as an example, in 1992 Sonopress produced the first CD in Mexico, entitled De mil colores (by Daniela Romo). In 1984 compact discs were opened to the world of computing, allowing storage of up to 700 MB.
The diameter of the central perforation of the compact discs was determined in 15 mm, when between meals, the creators were inspired by the diameter of the 10 cent guilder from Holland. In contrast, the diameter of compact discs is 12 cm, which corresponds to the width of the top pockets of men’s shirts, because according to Sony’s philosophy, everything had to fit there.
The three recordable media that rely on optical reading are: CD-ROM, CD-R, and CD-RW. CD ROM and CD-R can only be burned once. CD-WRs allow multiple reading and recording.
Although there may be variations in the composition of the materials used to make the discs, they all follow the same pattern: compact discs are made from a 1.2-millimeter thick disc of plastic polycarbonate, which a reflective layer of aluminum is added, used to obtain more longevity of the data, which will reflect the laser light (in the infrared spectrum range and therefore not visually appreciable); subsequently a protective layer of lacquer is added, which acts as a protector for the aluminum and, optionally, a label on the upper part.
Common printing methods on CDs are screen printing and offset printing. In the case of CD-R and CD-RW, gold, silver and their alloys are used, which due to their ductility allows lasers to record on it, something that could not be done on aluminum with low-power lasers.
The CD-Roms They are made up of a spiral track that has the same number of bits per centimeter in all its sections (constant linear density), to make better use of the storage medium, and not waste space as happens in magnetic disks. This is why when reading and writing a CD, as the laser beam moves away from the center of the disc, the speed must decrease, since in the center the spiral is shorter than in the edges. By alternating the speeds, it is achieved that the amount of bits read per second is constant in any section, be it in the center or at the edges. If this speed were constant, fewer bits per second would be read if the zone is closer to the center, and more if it is closer to the edges. All of this means that a CD rotates at a variable angular speed.
In order to achieve that the CDs have the same density in any section of the spiral, in the recording, the laser beam emitted by the head (which moves in a radial straight line from the center to the edge of the platter) generates the spiral at constant linear speed (CLV), this means that the number of recorded bits per second will be constant. But in order to achieve this, and to maintain a constant linear density and spiral track, it will be necessary for the CD to rotate at a variable angular speed (explained above). Therefore, by spinning a CD at a variable angular speed, and being written at a constant linear speed, the same amount of bits are written and read per second and per centimeter, whatever the position of the CD. Whereas each turn of the spiral will contain more or less bits depending on whether it is closer to the center or to the edge.
Standard CDs are available in different sizes and capacities, so we have the following variety of discs:
- 120mm (diameter) with 74-80 minutes of audio time and 650–700MB of data capacity.
- 120mm (diameter) with a duration of 90–100 minutes of audio and 800-875MB of data (not on the market today).
- 80mm (diameter), which were initially designed for CD singles. These can store about 21 minutes of music or 210 MB of data. They are also known as “mini-CDs” or “pocket CDs.”
A standard CD-ROM can hold 650 or 700 (sometimes 800) MB of data. The CD-ROM is popular for the distribution of software, especially multimedia applications, and large databases. A CD weighs less than 30 grams. To put CD-ROM memory in context, an average novel contains 60,000 words. Assuming that an average word has 10 letters – in fact it is considerably less than 10 letters – and each letter occupies one byte, a novel would therefore occupy 600,000 bytes (600 kB).
A CD can therefore contain more than 1000 novels. If each novel occupies at least one centimeter on a shelf, then a CD can hold the equivalent of more than 10 meters on the shelf. However, the textual data can be compressed ten times more, using compression algorithms, therefore a CD-ROM can store the equivalent of more than 100 meters of shelf.
Once the problem of storing the data has been solved, it remains to interpret it correctly. To do this, the companies that created the compact disc defined a series of standards, each of which reflected a different level. Each document was bound in a different color, giving name to each one of the ” Rainbow Books”.