CD and DVD Drives

How data is stored in a compact disk CD?


Wiki User

"Here's how the CD-ROM works, in a nutshell (I'm not going to go into the gory details of how the laser beams are manipulated within the drive because that can get complicated--there are in fact several slightly different ways that the internals work): A beam of light energy is emitted from an infrared laser diode and aimed toward a reflecting mirror. The mirror is part of the head assembly, which moves linearly along the surface of the disk. The light reflects off the mirror and through a focusing lens, and shines onto a specific point on the disk. A certain amount of light is reflected back from the disk. The amount of light reflected depends on which part of the disk the beam strikes: each position on the disk is encoded as a one or a zero based on the presence or absence of "pits" in the surface of the disk. This is discussed in more detail in the section on CD-ROM media. A series of collectors, mirrors and lenses accumulates and focuses the reflected light from the surface of the disk and sends it toward a photodetector. The photodetector transforms the light energy into electrical energy. The strength of the signal is dependent on how much light was reflected from the disk. Most of these components are fixed in place; only the head assembly containing the mirror and read lens moves. This makes for a relatively simplified design. CD-ROMs are of course single-sided media, and the drive therefore has only one "head" to go with this single data surface." Source(s):