The laser beam, which reads all the data on a CD, has to be very fine indeed. It is small enough to fit into one pit and land of a CD. Its wavelength is about 780 nm (nanometers), infrared light. It is beyond the visible spectrum of naked human eyes.
When a low-intensity infrared laser places a CD. Since the outside of a disc would spin faster than the inside, the scanning rate must be reduced as the laser moves from the inside to the outside. The rotation rate slows from about 500 rpm to 200 rpm (revolutions per minute). Two more lasers are sometimes used to help control the focus of the main laser and the rotation of the disc. The pits and the bumps (sometimes called lands or smooth areas) reflect the laser light differently, and the result is a binary code deciphered by the computer. This is done when a photodiode generates an electrical signal when there is not enough light energy to activate it. When the laser scores a pit area, the light is dispersed and the above effect is achieved. In binary code, pits are interpreted as "zeroes" and lands are interpreted as "ones". Digital-to-analog conversion translates the binary data into audio signals for reproduction.
Now, one must wonder with the multitude of possible things accomplish with the CD, how can a CD produced by one person be read by another with a different drive. The Universal Disc Format presented by the Optical Storage Technology Association (OSTA) has solved that problem and made reasonable communications with operating systems possible. It was written to be compatible with the ISO 9660 CD standard for file names and structures.