A DVD drive is an optical device. A DVD has the same diameter and half the thickness of a CD. It also has one spiral track on which data are stored. If this track is stretched, it will extend to over 12 kilometers. A DVD may have from one to four data layers with each layer storing millions of bits as tiny pumps and flat areas and with each layer being covered with a reflective metallic layer.

Similar to CDs and CD drives, DVDs and DVD drives can be read-only (DVD-ROM), recordable (two formats: DVD+R and DVD-R), and rewritable (three formats: DVD+RW, DVD-RW, and DVD-RAM). The concept of a DVD drive’s inner working is to a large extent similar to that of a CD drive. For instance, a DVD-ROM drive’s read head works as that of a CD-ROM drive but it has much more precision and it can focus on one or two data layers. Thus, a data layer pump diffuses a laser beam away from a sensor and this is interpreted as a 0, whereas a flat area reflects the beam into the sensor and this is interpreted as a 1.