How is data stored on a CD-ROM?

Answer 1

Data is recorded onto a CD in a clockwise spiral from the center. Its recorded and read in a series of lands and pits. Any land that the laser hits is reflected to the read head and is recorded as a 1 or a 0. They are counted in groups of 14 and then converted into standard 8-digit data.

A CD is built from a plastic (polycarbonate) substrate and a fine, reflective metallic film (24-carat gold or a silver alloy). The reflective layer is then covered with an anti-UV acrylic finish, creating a protective surface for data. Finally, an additional layer may be added so that data can be written on the other side of the CD as well.

The reflective layer contains tiny bumps. When the laser passes over the polycarbonate substrate, light is reflected off the reflective surface, but when the laser reaches a bump, that's what allows it to encode information.

This information is stored in 22188 tracks engraved in grooves (though it's actually just one track spiralling inward).

Commercially purchased CDs have already been pressed, meaning that the bumps have been created used plastic injected into a mold which contains the desired pattern in reverse. A metallic layer is then affixed onto the polycarbonate substrate, and this layer is itself covered with a protective coating.

Answer 2

Recordable compact discs, CD-Rs, are injection molded with a "blank" data spiral. A photosensitive dye is then applied, after which the discs are metalized and lacquer-coated. The write laser of the CD recorder changes the color of the dye to allow the read laser of a standard CD player to see the data, just as it would with a standard stamped disc. The resulting discs can be read by most CD-ROM drives and played in most audio CD players.

CD-R recordings are designed to be permanent. Over time the dye's physical characteristics may change, however, causing read errors and data loss until the reading device cannot recover with error correction methods. The design life is from 20 to 100 years, depending on the quality of the discs, the quality of the writing drive, and storage conditions. However, testing has demonstrated such degradation of some discs in as little as 18 months under normal storage conditions.[26][27] This failure is known as CD rot. CD-Rs follow the Orange Book standard.

Answer 3

Pits in a thin sheet of metal between two sheets of plastic. In commercial mass produced CD-ROMs the first sheet of plastic is molded with bumps at the locations where the pits are to be. A thin layer of aluminum is vapor deposited over this sheet of plastic, the bumps in the plastic form pits in the aluminum. The second layer of plastic is then molded over the metal to protect it. This forms all the pits in one step.

In home made and low volume production CDs a CD-R with a thin layer of tantalum molded between the plastic sheets gets the pits burned one at a time. This is slower but cheaper to do for small quantities.
650mb to 700mb

http://en.wikipedia.org/wiki/CD

Answer 4

The optical drive uses electromagnetic waves or laser light to read or write data to or from optical discs. Optical discs are composed of millions of small bumps and indentations. Waves or lights from the optical drive read these indentations and bumps as zeros and ones, or binary code. The computer interprets the code and can then translate it into pixels, creating images, and electronic signals, producing sound.

Answer 5

The information is stored either in the lead area of the CD, where there is roughly 5 kilobytes of space available or in the subcode.