Binary-code compatibility

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Binary-code compatibility (binary compatible or object-code compatible) is a property of a computer system, meaning that it can run the same executable code, typically machine code for a general-purpose computer central processing unit (CPU), that another computer system can run. Source-code compatibility, on the other hand, means that recompilation or interpretation is necessary before the program can be run on the compatible system.

For a compiled program on a general operating system, binary compatibility often implies that not only the CPUs (instruction sets) of the two computers are binary compatible, but also that interfaces and behaviours of the operating system (OS) and application programming interfaces (APIs), and the application binary interfaces (ABIs) corresponding to those APIs, are sufficiently equal, i.e. "compatible".

A term like backward-compatible usually implies object-code compatibility. This means that newer computer hardware and/or software has (practically) every feature of the old, plus additional capabilities or performance. Older executable code will thus run unchanged on the newer product. For a compiled program running directly on a CPU under an OS, a "binary compatible operating system" primarily means application binary interface (ABI) compatibility with another system. However, it also often implies that APIs that the application depends on, directly or indirectly (such as the Windows API, for example), are sufficiently similar. Hardware (besides the CPU, such as for graphics) and peripherals that an application accesses may also be a factor for full compatibility, although many hardware differences are hidden by modern APIs (often partly supplied by the OS itself and partly by specific device drivers).

In other cases, a general porting of the software must be used to make non-binary-compatible programs work.

Binary compatibility is a major benefit when developing computer programs that are to be run on multiple OSes. Several Unix-based OSes, such as FreeBSD or NetBSD, offer binary compatibility with more popular OSes, such as Linux-derived ones, since most binary executables are not commonly distributed for such OSes.

Most OSes provide binary compatibility, in each version of the OS, for most binaries built to run on earlier versions of the OS. For example, many executables compiled for Windows 3.1, Windows 95 or Windows 2000 can also be run on Windows XP or Windows 7, and many applications for DOS ran on much newer versions of Windows up to Windows 10 for as long as the NTVDM was supported.