DVD-R (pronounced "DVD dash R") and DVD+R (pronounced "DVD plus R") are nearly identical formats. The discs look the same and are both supported by most DVD-ROM drives and DVD burners. The only difference between the formats is the way they determine the location of the laser beam on the disc. DVD-R discs use tiny marks along the grooves in the discs, called land prepits, to determine the laser position. DVD+R discs do not have land prepits, but instead measure the "wobble frequency" as the laser moves toward the outside of the disc.