macOS Under the Hood

macOS is a polished Unix machine - Darwin and the XNU kernel underneath, a real Unix filesystem hiding beneath the Finder, apps that are secretly folders, and a Terminal that feels like Linux because it nearly is.

1. macOS Is Unix macOS is built on Darwin, an open-source Unix foundation with the XNU kernel and a BSD heritage - which is why the Terminal feels like Linux and why a real Unix filesystem (/, /usr, /etc, /Users) sits underneath Finder's friendly view.
2. Apps, Bundles & Where Things Live A .app is actually a folder (a bundle), not a single file; macOS has several Library folders (system, /Library, and ~/Library) holding preferences as plist files, caches, and application support; and Homebrew is how you install real CLI tools.
3. Under the Surface The Terminal runs zsh, macOS's default shell; launchd is the service manager that starts and supervises everything (macOS's answer to Linux's systemd); and Gatekeeper, SIP, and permission prompts are the security layers a power user meets - plus where macOS really differs from Linux.