POSIX, XNU

POSIX represents a portable operating system interface (Portable Operating system Interface, abbreviated as POSIX), and the POSIX standard defines the interface standards that the operating system should provide for applications. is the generic term for the series of API standards that IEEE defines for software to run on a variety of UNIX operating systems, formally referred to as IEEE 1003, and the International standard name is ISO/IEC 9945.
The POSIX standard is intended for software portability at the source code level. In other words, a program written for a POSIX-compliant operating system should be compiled and executed on any other POSIX operating system, even from another vendor.

XNU, an operating system kernel developed by Apple computers, is used in Mac OS X. It is part of the Darwin operating system and is released as a free and open source software along with Darwin. XNU is an abbreviation for x is not UNIX. Darwin is the operating system portion of Mac OS X and iOS operating environments.

History
XNU was first developed by next company in order to nextstep the operating system. It is a hybrid core (Hybrid kernel), combined with the development of the Carnegie Mellon University of Mach 2.5, 4.3BSD, with an object-oriented application interface called Driver Kit.
After Apple's acquisition of Next, Xnu's Mach microkernel was upgraded to the part of Mach 3.0,bsd to freebsd,driver kit to I/O kit, a set of application interfaces written in C + +.

POSIX, XNU