Data position measurement (DPM) is a copy protection mechanism that operates by measuring the physical location of data on an optical disc. Stamped CDs are perfect clones and always have the data at the expected location, while a burned copy would exhibit physical differences. DPM detects these differences to identify user-made copies. DPM was first used publicly in SecuROM 4.7.[1]
DPM can be observed and subsequently encoded into a Recordable Media Physical Signature. In concert with emulation software, RMPS can reproduce the effects of DPM, thereby appearing as an original disc and fooling the protection mechanism. This technique was pioneered by Alcohol 120%, for which it created the .mds file format.