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. Most current DVD drives support both the + and - standards, while few support the DVD-RAM standard, which is not directly compatible with standard DVD drives.
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 in real time, that is, 1X speed.
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. DVD burner lasers often peak at about 100-400 mW in continuous wave (some are pulsed).