Actually UNIX kind of plays the role of C runtime, but when the time for standardizing C came, they could only make into ANSI C features that were common across multiple hardware and OSes back in the late 80&#x27;s.<p>So what was left out of ANSI C, is what became POSIX. Making any OS with ANSI C + POSIX compliant compatible with the original UNIX systems.<p>But unlike other programming languages, on C&#x27;s case the evolution in terms of standard libraries stopped there.