Fat binary

Fat binary software, as first implemented by Apple Computer in 1994, contains both 68k and PowerPC code to facilitate the transition from classic Macintosh computers using Motorola processors to Power Macintosh systems using PowerPC processors.

Description
Many applications written for 68k systems ran transparently on the new PowerPC systems under an evolving emulation scheme, but emulated code generally runs slower than native code. Applications released as "fat binaries" took up more storage space, but they ran at full speed on either platform. This was achieved by packaging both a 68000-compiled version and a PowerPC-compiled version of the same program into their executable files. The older 68K code (CFM-68K or classic 68K) continued to be stored in the resource fork, while the newer PowerPC code was contained in the data fork, in PEF format.

Fat binaries were larger than programs supporting only the PowerPC or 68k, which led to the creation of a number of utilities that would strip out the unneeded version. In the era of small hard drives, when 80 MB hard drives were a common size, these utilities were sometimes useful, as program code was generally a large percentage of overall drive usage, and stripping the unneeded members of a fat binary would free up a significant amount of space on a hard drive.

Latter implementations

 * Universal binary, used during Apple's transition from PowerPC to Intel processors.
 * Universal 2, used during Apple's transition from 64-bit Intel to Apple processors.