- Not to be confused with the MGT format which is used with the DSK file extension for SAM Coupé disks.
The DSK format is a standard for storing floppy disk images. 
An extended version of the format called EDSK was developed by Marco Vieth, Ulrich Doewich, and Kevin Thacker to enable images of disks utilizing certain copy protection schemes. The EDSK specification includes further extensions proposed by John Elliot and Simon Owen to store more information about the floppy disk controller state and support even more copy protection schemes respectively. 
Both format specifications are also available on the CPC Wiki