In Mac OS X, DMG (Disk Mounted Graphics) files are dealt like real disks. You can mount these image files as normal hard drive volume. This file format enables you file compression as well as secure password protection and thus serves both file distribution and security functions. You can easily create DMG files with the help of Disk Utility in Mac OS X 10.3 and later versions. You can easily access data from DMG files after mounting them. However, in some cases, such files can not be mounted and you can not access data from them. At this point, you may lose your valuable data and need Mac Data Recovery to retrieve the lost data.