MacOS implements a native image mounting mechanism as part of its random access disk device abstraction. The command "hdiutil attach -imagekey diskimage-class=CRawDiskImage -nomount <filename>" causes a block device to appear in "/dev" as a regular disk device and subdevices for recognized partitions. Reads from and writes to those devices are sent to a user-mode helper process, which reads the data from the file or writes it to the file. In the user interface it is automatically activated by opening the disk image. MacOS can handle disk (.dmg or .iso), CD-ROM or DVD images in various formats.