A self mounting image is a disk image

Disk image

A disk image is a single file or storage device containing the complete contents and structure representing a data storage medium or device, such as a hard drive, tape drive, floppy disk, CD/DVD/BD, or USB flash drive, although an image of an optical disc may be referred to as an optical disc image...

 format, commonly found on the Macintosh Classic

Macintosh Classic

The Macintosh Classic was a personal computer manufactured by Apple Computer. Introduced on October 15, 1990, it was the first Apple Macintosh to sell for less than US$1,000. Production of the Classic was prompted by the success of the Macintosh Plus and the SE...

 platform, that is encapsulated in an application

Application software

Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...

 that mounts it as a file system. When downloaded from the Internet, they are often in a BIN

BIN

Bin and similar can mean:*A kind of receptacle, especially a wastebin or recycling bin.*A "bin box" or pallet sized container: bulk box-bin:"bin" can mean:*/bin, a common Unix directory...

, BinHex

BinHex

BinHex, short for "binary-to-hexadecimal", is a binary-to-text encoding system that was used on the Mac OS for sending binary files through e-mail. It is similar to Uuencode, but combined both "forks" of the Mac file system together, along with extended file information...

 or StuffIt

StuffIt

StuffIt is a family of computer software utilities for archiving and compressing files on the Macintosh and Microsoft Windows platforms: it was originally produced for the Macintosh. An old version for Linux and Sun Solaris 2.7 or later is also available...

 file. Despite being an application, they often have a .smi file extension. Disk Copy

Disk Copy

Disk Copy was the default utility for handling disk images in System 7 through Mac OS X 10.2 . In later versions of Mac OS X it has been replaced by DiskImageMounter for mounting the images and Disk Utility for creating them.Although the last official public release of Disk Copy for Mac OS 9 was...

, the application commonly used to handle disk images in Mac OS

Mac OS

Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...

 was an optional program not part of the standard installation.

Self mounting images have fallen out of favor with the arrival of Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

. All copies of Mac OS X have DiskImageMounter

DiskImageMounter

DiskImageMounter is the utility that handles mounting disk images in Mac OS X, starting with version 10.3. Like BOMArchiveHelper it has no GUI when double-clicked; in fact, doing so does nothing. It is found in /System/Library/CoreServices/DiskImageMounter.app...

, the utility for mounting disk images.