Originally, DVD recorders supported one of three standards: DVD-RAM, DVD-RW (using DVD-VR), and DVD+RW (using DVD+VR), none of which are directly compatible. As a general rule, however, most current drives support both the + and - standards, while few support the DVD-RAM standard, which is not directly compatible with standard DVD readers.
Recording speed is generally denoted in values of X (similar to CD-ROM usage), where 1X in DVD usage is equal to 1.321 MB/s, roughly equivalent to a 9X CD-ROM. In practice, this is largely confined to computer-based DVD recorders, since standalone units generally record inreal time, that is, 1X speed.
DVD recorders use a laser (usually 650 nm red) to read and write DVDs. The reading laser is usually not stronger than 5 mW, while the writing laser is considerably more powerful. The faster the writing speed is rated, the stronger the laser is. DVD burner lasers often peak at about 100-400 mW in continuous wave (some are pulsed). Some laser hobbyists have discovered ways to extract the laser diode from DVD burners and modify them to create laser apparatus that can cause burning.