Glossary
XNU
The kernel that runs macOS, iOS, watchOS, tvOS, and visionOS — Mach core, BSD personality, IOKit drivers, all in one binary.
XNU ("X is Not Unix") is Apple's kernel. It's a hybrid: a Mach microkernel core, a FreeBSD-derived BSD layer for POSIX, and the IOKit C++ object model for drivers — all linked into a single binary that boots and runs as a monolithic kernel.
Apple publishes the full source at apple-oss-distributions/xnu, refreshed for each macOS release.
apple-oss-distributions/xnuREADME.mdThe repo's own README — start here for the top-level tour.View on GitHub(line —)Each macOS release tags a corresponding XNU version (e.g. macOS 14.x ships xnu-10063.101.17). The same kernel source builds for both Apple Silicon and the remaining Intel platforms, plus Apple's mobile OSes — the differences live in subdirectories under osfmk/ and conditional compilation, not in separate trees.