A file with the .dmg extension is a type of Macintosh OS X disk image. The dmg format includes many options including various volume types (HFS, HFS+, HFSX, etc.), several compression options, encryption (password protection) and file spanning (segmenting). Compressed dmg files are generally read-only.

Dmg files are often used for Mac software installations and general data exchange. Since internal compression is supported, this format is sometimes used instead of general compression archive formats like zip or sit.

While this format is generally exclusive to the Mac, our software TransMac can create, open and compress unencrypted dmg files on a PC in Windows. Please note that even though TransMac can extract any file from a dmg and copy it to a PC drive, Windows will not be able to install or run Mac software. Only certain data files (image, video, text, html, sound, etc.) will be usable in Windows, and even then only if you have the proper applications to open them.