-The laser that is used on a CD-ROM is yellow laser to read data unlike the DVD that uses a red laser. The idea is that we need to be able to see bits that are in a tighter area on the disc itself. The red laser has a shorter wavelength and can squeeze into those bits. Now how is this stuff reflected back so it may be read? The undercoating of the disc is silver and very reflective. When the laser is on low power it can read the bits of the coating. When the laser is on increased power it can read the less reflective and semitransparent gold layer. So we are making two layers and have more information in one area. The same basic concept applies to the CD-ROM when it comes to reading the land to pit scheme of 0's and 1's.
