The Berkeley Software Distribution (BSD) part of the kernel provides the Portable Operating System Interface (POSIX) application programming interface (API, BSD system calls), the Unix process model atop Mach tasks, basic security policies, user and group ids, permissions, the network protocol stack (protocols), the virtual file system code (including a file system independent journaling layer), several local file systems such as Hierarchical File System (HFS, HFS Plus (HFS+)) and Apple File System (APFS), the Network File System (NFS) client and server, cryptographic framework, UNIX System V inter-process communication (IPC), audit subsystem, mandatory access control, and some of the locking primitives.[7] The BSD code present in XNU has been most recently synchronised with that from the FreeBSD kernel. Although much of it has been significantly modified, code sharing still occurs between Apple and the FreeBSD Project as of 2009.[8]
> Darwin - which consists of the XNU kernel, IOkit (a driver model), and POSIX compatibility via a BSD compatibility layer - makes up part of macOS (as well as iOS, tvOS, and others) includes a few subsystems (such as the VFS, process model, and network implementation) from (older versions of) FreeBSD, but is mostly an independent implementation.
