Editing Fat binary (section)

{{Short description|Combined executable file for multiple processor types or operating systems}}
{{Distinguish|Portable executable|Portable application}}
{{Use dmy dates|date=April 2019|cs1-dates=y}}
{{Use list-defined references|date=December 2021}}
A '''fat binary''' (or '''multiarchitecture binary''') is a computer [[executable program]] or [[library (computing)|library]] which has been expanded (or "fattened") with code native to multiple [[instruction set]]s which can consequently be run on multiple processor types.<ref name="Devanbu-Fong-Stubblebine_1998"/> This results in a file larger than a normal one-architecture binary file, thus the name.

The usual method of implementation is to include a version of the [[machine code]] for each instruction set, preceded by a single [[entry point]] with code compatible with all operating systems, which executes a jump to the appropriate section. Alternative implementations store different executables in different [[Fork (file system)|forks]], each with its own entry point that is directly used by the operating system.

The use of fat binaries is not common in [[operating system]] software; there are several alternatives to solve the same problem, such as the use of an [[installer]] program to choose an architecture-specific binary at install time (such as with [[Android (operating system)|Android]] multiple [[Android Package|APK]]s), selecting an architecture-specific binary at runtime (such as with [[Plan 9 from Bell Labs|Plan 9]]'s [[union directory (Plan 9)|union directories]] and {{anchor|GNUstep fat bundle}}[[GNUstep]]'s fat bundles),<ref name="Pero_2008"/><ref name="GNUstep_2009"/> distributing software in [[source code]] form and [[compiler|compiling]] it in-place, or the use of a [[virtual machine]] (such as with [[Java Virtual Machine|Java]]) and [[just-in-time compilation]].<!-- Commenting the following statement out: All of these solutions have their downsides however, notably if the user attempts to move such a program to a new machine during an upgrade. Neither a source distribution nor a virtual machine would have a problem moving to a new machine assuming a compiler or virtual machine implementation was available for the new machine. -->