A DMG file is a mountable disk image created in Mac OS X. It contains raw block data typically compressed and sometimes encrypted. DMG files are commonly used for OS X software installers that are downloaded from the Internet and mounts a virtual disk on the desktop when opened.
The DMG format replaces the older .IMG file format used in Mac OS Classic. DMG disk images can be opened using the Apple Disk Utility that is bundled with Mac OS X on Apple computers.
DMG files are Mac-specific and are not intended for use in Windows. However, Windows Daemon Tools may be able to mount virtual drives from some DMG image files. Other utilities may also be able to convert DMG files to a format that can be recognized by Windows.