CD Storage Information

Compact Disc

A Compact Disc (CD) is an optical disc used to store digital data, originally developed for storing digital audio. The CD, introduced in 1982, remains the standard playback format for commercial audio recordings. An audio compact disc consists of one or more stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. Standard compact discs have a diameter of 120 mm or 80 mm. The 120 mm discs can hold approximately 80 minutes of audio. The 80 mm discs, sometimes used for CD singles, hold approximately 20 minutes of audio. Compact disc technology was later adapted for use as a data storage device, known as a CD-ROM, and to include record-once and re-writable media (CD-R and CD-RW). CD-ROMs and CD-Rs remain widely used technologies in the personal-computer industry as of 2006. The CD and its extensions have been extremely successful: in 2004, the annual worldwide sales of CD-Audio, CD-ROM, and CD-R reached about 30 billion discs.

Physical details

Compact discs are made from a 1.2 mm thick disc of very pure polycarbonate plastic. A thin layer of Super Purity Aluminium is applied (or rarely gold, used for its data longevity, such as in some limited-edition audiophile CDs) to the surface to make it reflective, which is protected by a film of lacquer. The lacquer can be printed with a label. Common printing methods for compact discs are silkscreening and offset printing. CD data is stored as a series of tiny indentations (pits), encoded in a tightly packed spiral track of pits moulded into the top of the polycarbonate layer. The areas between pits are known as 'lands'. Each pit is approximately 100 nm deep by 500 nm wide, and varies from 850 nm to 3.5 ìm of length. The spacing between the tracks, the pitch, is 1.6 ìm. A CD is read by focusing a 780 nm wavelength semiconductor laser through the bottom of the polycarbonate layer. The difference in height between pits and lands leads to a phase difference between the light reflected from a pit and from its surrounding land. By measuring the intensity with a photodiode, one is able to read the data from the disc. The pits and lands themselves do not directly represent the zeroes and ones of binary data. Instead, Non-return-to-zero, inverted encoding is used: a change from pit to land or land to pit indicates a one, while no change indicates a zero. This in turn is decoded by reversing the Eight-to-Fourteen Modulation used in mastering the disc, and then reversing the Cross-Interleaved Reed-Solomon Coding, finally revealing the raw audio data stored on the disc. Disc shapes and diameters In reverse fashion to that of a vinyl record, the digital data on a CD begins at the center of the disc and proceeds outwards to the edge, which allows adaptation to the different size formats available. Standard CDs are available in two sizes. By far the most common is 120 mm in diameter, with a 74-minute audio capacity and a 650 MB data or an 80-minute audio capacity and a 700 MB data.

CD Storage Rack

The capacity of a device to hold and retain data

With all the information about CD Discs and how they are used, we are definitely in the business of finding a place to store them. CD’s have become a large part of our lives at work and at play and where we store them as become vital to us. CD Cabinets have become a part of our furniture. At work we have CD Storage Racks that can be placed right at our fingertips for easy access. We even carry CD’s with us wherever we go filled with our favorite music or important data making it necessary to have a portable CD case available to us. We sell all types of transportable CD cases in metal, plastic, wood and even cloth visors for your car. There is even CD Wall storage available that allows us to hang our favorite jewel cases as pieces of art. CD Storage is as necessary as a good pillow on a strong bed; it comforts us and leaves us with a restfulness knowing that our CD’s are secure and in order.