When I said:

This software is a very important part of a computer system: no software can run without it.

I was talking about the FACT, that today, ALL computer systems are proprietary plateforms, because the processor and its microcode (and most of time time if not every time the BIOS is proprietary).

I didn't ask you to cite me out of context; I asked to prove the countrary.

If you can't prove the countrary, it means that in any case, we still need today, sometimes, to make compromises, in the hope that they won't be needed anymore in the future because someone took the time or gave the money to reimplement it as libre software.