CD Disc

pictures, photos, facts and information on CD Disc (Mediums)

CD Disc ( 640x480 )
Camera Maker:Panasonic
Camera Model:DMC-FZ5
Shutter Speed:1/100 s
Exposure Bias Value:0.0 eV
Focal Length:16.2 mm
CD, which literally means a compact disc, is a type of a disc recordable media. The First CD disc was presented to Europe and Japan in 1982 fall. Already in 1990 year the sales of CD discs achieved 1 Billion pieces. CDs have a thickness of 1.2 millimeters and their diameter is commonly 12 centimeters, but it can be also 8 centimeters.

One CD can store up to 74 minutes of music. This means that are 44,100 samples/channel/second x 2 bytes/sample x 2 channels x 74 minutes x 60 seconds/minute that gives us the total number of 783,216,000 bytes. 780 millions bytes is much more than what can fit into more than 500 diskettes, and furthermore one diskette is only slightly more expensive than a CD disc.

The thickness of a CD is mostly divided into four layers. The largest layer is of polycarbonate plastic. In the process of fabrication is this layer impressed very small bumps that create an extreme long spiral (is only 12nm deep) which goes along the whole CD. The spiral is approximately 6 kilometers long. The spiral is filled with an expensive dye. It is the most expensive part of a CD. One kilogram of this dye in solid state costs several thousands of dollars. The second layer consist of aluminum, it should cover the bumps. The next layer is from acryl and has a protective function. The last layer is the cover of the CD with various possible motives printed on or it can be clean.

The CD has a durability between twenty and thirty years. In the case of rewritable CD discs it’s less. A new effect is the “CD mould” which is a rust of the aluminum layer.

The reading from the CD is following- the CD disc begins to rotate from the speed of 200 rotations/minute (the reading speed 1x) up to a speed of 10000 rotations/minute (reading speed 52x), a light with an wavelength of 780 nanometers (laser) is emitted towards the data track, the surface reflects the light in the reading device, but the pits in the surface are reflecting the light away from it. After the receiving of the laser reflections calculates the computer the sequence and identifies it as a code that he know and the data go to further processing.

The CD discs are without doubt written with big letters in the history of the digital media.
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