The UNIX operating system written by IBM. Current version is 4.3.1. Previous notable versions are 4.2, 4.1.4, and 3.2.5. In 4.3.1, they changed a bunch of stuff in includes/arpa/inet.h which made lots of things I tried to compile hork and utterly fail.

AIX should be pronounced "aches," as after working with it, your head will certainly ache.

Fortunately, IBM is supposedly working on a Linux port for their RS6000 machines.