File with a .DSK extension contains a disc image, it is a general extension, utilised in different specifications by a variety of programs. Therefore, a DSK file created with an application might not be possible to be opened in a different program also utilising this extension. DSK file may contain image of CD, DVD, floppy or a whole hard drive.

The content of a DSK file can be compressed, due to the fact that such images are often used to archive discs in order to save disc space. Software which enables creation of disc images (for instance: PowerISO), can also enable mounting them within an operating system in the way so that they are perceived as physical disc plugged into the computer.