How does a CD work?

Question

I know that a CD can play music, burn, excetera... but is all of the information in the middle of the CD? So does a matchine scan the CD?

Answer 1

A Compact Disc is made from a 1.2 mm thick disc of almost pure polycarbonate plastic and weighs approximately 16 grams.

A thin layer of Super Purity Aluminium (or rarely gold, used for its data longevity, such as in some limited-edition audiophile CDs) is applied to the surface to make it reflective, and is protected by a film of lacquer.

The lacquer is normally printed directly and not with an adhesive label. Common printing methods for compact discs are screen-printing and offset printing. CD data is stored as a series of tiny indentations (pits), encoded in a tightly packed spiral track 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 m in length.

The spacing between the tracks, the pitch, is 1.6 ?m. 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 that from its surrounding land.

By measuring the intensity with a photodiode, it is possible to read the data from the disc. The pits and lands themselves do not directly represent the zeros 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 data stored on the disc.

Pits are much closer to the label side of a disc so that defects and dirt on the clear side can be out of focus during playback. Discs consequently suffer more damage because of defects such as scratches on the label side, whereas clear-side scratches can be repaired by refilling them with plastic of similar index of refraction




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Answer 2

Understanding the CD: Material
As discussed in How Analog and Digital Recording Works, a CD can store up to 74 minutes of music, so the total amount of digital data that must be stored on a CD is:

44,100 samples/channel/second x 2 bytes/sample x 2 channels x 74 minutes x 60 seconds/minute = 783,216,000 bytes
To fit more than 783 megabytes (MB) onto a disc only 4.8 inches (12 cm) in diameter requires that the individual bytes be very small. By examining the physical construction of a CD, you can begin to understand just how small these bytes are.

A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of an injection-molded piece of clear polycarbonate plastic. During manufacturing, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. We'll return to the bumps in a moment. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic. A cross section of a complete CD (not to scale) looks like this:


Cross-section of a CD

Answer 3

Check this article: How Cds Work

¨As discussed in How Analog and Digital Recording Works, a CD can store up to 74 minutes of music, so the total amount of digital data that must be stored on a CD is:

44,100 samples/channel/second x 2 bytes/sample x 2 channels x 74 minutes x 60 seconds/minute = 783,216,000 bytes
To fit more than 783 megabytes (MB) onto a disc only 4.8 inches (12 cm) in diameter requires that the individual bytes be very small. By examining the physical construction of a CD, you can begin to understand just how small these bytes are. ...

...The CD player has the job of finding and reading the data stored as bumps on the CD. Considering how small the bumps are, the CD player is an exceptionally precise piece of equipment.... ¨

Answer 4

A compact disk reads codes that are created by light reflecting (or not reflecting) from the disk. These codes are represented by "0" and "1". There are many different kinds of codes such as "American Standard Code of Information Interchange". These different codes can create (or recreate) almost anything that a computer can need to run almost any program. There is a directory with different files and file extensions which include the physical arrangement of where the data files begin and end on the compact disk. The read (write) mechanism goes to the place where the directory is located to scan that data into the main memory. Then the read (write) mechanism goes to whatever part of the disk contains the data files which are needed.

Answer 5

it works very much the same as an old record, with the record there was the track (a groove that ran in a spiral around the disc), the track contained the sound information by varying the depth of the groove the sound was retrieved by running a needle through the groove and measuring the movement.
with a CD the the groove is much smaller and the needle that reads it is a laser beam

Answer 6

you first make a playlist of the songs you want on the CD then insert the cd and interior the backside appropriate nook while viewing the playlist it ays burn to disk click that and away you flow =)

Answer 7

a laser reads the cd

Answer 8

Duno

Answer 9

who cares how it works.. just buy a cd player or put it in ur cpu and USE it!!!!