It's not what the implementation uses, but "which conventions does the call interface assume" you can use Pascal to create an operating system with a system int

It's not what the implementation uses, but "which conventions does the call interface assume" you can use Pascal to create an operating system with a system interface that benefits Fortran. (I know too little about Fortran to describe what that would look like) With C and Unix the issue of course is that both were developed around the same time by the same people for working together.