I would note that system calls only form an external API if the developer says they are an external API. Which it is for Linux but for other OSes the external A

I would note that system calls only form an external API if the developer says they are an external API. Which it is for Linux but for other OSes the external API is a C library, kernel32, etc. But right and wrong aside, there's the practical matter of reality. You can't simply pretend everything works how you want them to. At the end of the day you have to deal with how they actually work.