.dcm

The DCM file extension is a back-up tracking file that is used with “My Book” by the Western Digital Corporation. The back-up software that Western Digital delivers with their “My Book” create DCM files to keep track of changes in text-based files. If the end-user creates a backup text file, the back up software of the “My Book” creates an XML file with a DCM extension to enable the software to see whether the original text file has been changed or not.