.harddisk is Boxer for Mac harddisk image
Key Features: .HARDDISK File Extension
What is an .HARDDISK file?
The harddisk file extension is associated with the Boxer for Mac, an emulator of MS-DOS operating system for OS X (macOS) operating system aimed on old DOS computer games.
The harddisk file is container with game data stored on Boxer virtual hard drive.
The harddisk file can be found in .boxer container.