XNU (X is Not Unix) is the name of the kernel that is used in the free operating system Darwin. Darwin forms the basis of Apple's operating system OS X XNU is released as free software under Version 2 of the Apple Public Source License ( APSL ).

Kernel design

XNU is a hybrid kernel, consisting of parts of the Mach 3.0 microkernel and monolithic kernel in FreeBSD 5.x (Darwin 7.x).

In the BSD part of the multi-user system ( user IDs, rights ), the TCP / IP stack ( the firewall ), synchronization and allocation process is controlled. The Mach - part is responsible for multitasking, memory management and error handling. The I / O Kit manages Plug and Play, hot plugging, energy management and extension management.


The kernel was originally developed by NeXT for the NeXTSTEP operating system. NeXT was acquired by Apple in late 1996.