POSIX and SVR

POSIX is short for portable operating system interface of UNIX, "portable UNIX operating system interface ". It defines a minimum set of UNIX operating system interfaces.
The birth of POSIX is inseparable from the Development of Unix. with the participation of various commercial companies, the development of UNIX versions is extremely chaotic, and the compatibility of UNIX versions has become a big problem. Therefore, the emergence of POSIX defines a group of the smallest UNIX operating system interfaces. As long as applications program using this interface, they can ensure normal operation in various versions of UNIX systems. Naturally, each Unix Version has a big difference in the implementation of this write interface, but this difference does not affect the functions of the program, and the performance may be affected to a certain extent.

SVR (System V release) is the most influential UNIX branch in the Development of UNIX. A total of four versions are available: Version 1, 2, 3, and 4. The most successful version is version 4, which sometimes becomes svr4.

POSIX and SVR are currently the two most influential UNIX interfaces. The implementation of Linux inherits the two standards. Because SVR appeared earlier, many interface design ideas and implementation methods are outdated from today's point of view. Therefore, use POSIX interfaces whenever possible.