The differences between CDs and DVDs are data density and disc construction. A standard DVD holds 4.7 gigabytes of data, whereas a standard CD holds 700 megabytes of data.
The data on CDs and DVDs is recorded in a spiral that starts at the center of the disc. DVDs hold more data because they have a longer spiral on which to record data. This is made possible through the use of a narrower laser.
CDs are made from a single layer of polycarbonate with an aluminum recording layer on the top of the disc. DVDs are made from two thin layers of polycarbonate with an aluminum recording layer between the polycarbonate layers.