Data Position Measurement (DPM) is a copy protection

Copy protection

Copy protection, also known as content protection, copy obstruction, copy prevention and copy restriction, refer to techniques used for preventing the reproduction of software, films, music, and other media, usually for copyright reasons.- Terminology :Media corporations have always used the term...

 mechanism that operates by measuring the physical location of data on an optical disc

Optical disc

In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...

. 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

SecuROM

SecuROM is a CD/DVD copy protection and digital rights management product developed by Sony DADC. SecuROM aims to resist home media duplication devices, professional duplicators, and attempts at reverse engineering software. It is most often used for commercial computer games running under the...

 4.7.

RMPS

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.