A Mirror Disk File may be accompanied by a media descriptor sidecar file. This optional binary file (with file extension.mds) contains metadata about an imaged optical disc, including a delineation of where disc layers begin and end ("layer breaks"), and which portions of the MDF belong in which disc layer. The MDS file also stores the location and value of the layer breach bit, a CD/DVD copy protection mechanism. The MDS file is comparable to the CloneCD Control File and cue sheet (.cue) file formats. However, their capabilities are not identical; also the cue sheet is a text file format.