I think the meaning and the boundary has changed over time, but one of the most consistent features/requirements for a systems programming language is "embedabi

I think the meaning and the boundary has changed over time, but one of the most consistent features/requirements for a systems programming language is "embedability": - functions that are called from a different language, like how parts of NumPy are written in C - code that runs in kernel space - code that runs on tiny little devices that don't really have an OS at all In theory almost any language can do those things, but for a variety of reasons in practice we only use a small set of languages to do them.