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Mach-O

Mach-O, short for Mach object file format, is a file format for executables, object code, shared libraries, dynamically-loaded code, and core dumps. A replacement for the a.out format, Mach-O offers more extensibility and faster access to information in the symbol table.

Mach-O is used by most systems based on the Mach kernel. NeXTSTEP, OS X, and iOS are examples of systems that have used this format for native executables, libraries and object code.