Анонимные аналитики опеннета знают что в OS X осталось от BSD даже не читая спеков и документации

XNU's BSD component uses FreeBSD as the primary reference codebase (although some code might be traced to other BSDs). Darwin 7.x (Mac OS X 10.3.x) uses FreeBSD 5.x. As mentioned before, BSD runs not as an external (or user-level) server, but is part of the kernel itself. Some aspects that BSD is responsible for include:

process model
user ids, permissions, basic security policies
POSIX API, BSD style system calls
TCP/IP stack, BSD sockets, firewall
VFS and filesystems (see Mac OS X Filesystems for details)
System V IPC
crypto framework
various synchronization mechanisms