title: Why POSIX is called "Portable Operating System Interface"?
body: <p>I have searched hard but still confused why POSIX is called "Portable Operating System Interface", what I learned is that it is some threading library for Unix environment, because when you need to use it under windows you have to use cygwin or "Windows Services of Unix", etc. That's why I am confused why it is called Portable OSIX.  I am a professional C/C++ programmer in Windows domain but new in Unix/Linux. Thanks for your answers in advance.</p>