Data Position Measurement
(DPM) is a copy protection
method that controls the exact position of data on a CD
. Stamped CDs are perfect clones and have the data always at the same position, whereas writable media differ from each other. DPM detects these little physical differences to efficiently protect against duplicates. SecuROM
4 and later uses this protection method.
DPM can be circumvented by using suitable CD burning software (Alcohol 120% was the pioneer in this field) and a compatible CD burner: the disk must first be read with the DPM option enabled, and the copy must then be burned with Recordable Media Physical Signature (RMPS) data attached to the image; Alcohol 120% uses the media descriptor image format (.mds) to do so.