Mach-O (universal/fat) file format

A macOS universal (fat) Mach-O binary bundling multiple architectures.

MIME type: application/x-mach-binary
Extensions: .dylib, .bundle
Category: Executables & bytecode

Magic-number signature

0x00000000

CAFEBABE

····

'CAFEBABE' fat magic

About the Mach-O (universal/fat) format

A universal (fat) binary concatenates several Mach-O slices — say arm64 and x86-64 — so one file runs on multiple CPUs. It starts with CA FE BA BE, the same magic as a Java class file, disambiguated by the fields that follow.

Related formats

Mach-O executable
Java class file
ELF executable

Have a file that might be Mach-O (universal/fat)? Identify it with the File Type Identifier — it reads the magic number locally, nothing is uploaded. Or browse all formats.