Argument passing is, or was, defined in the "argument association" section of the standard, which obviously doesn't preclude implementing by reference. I don't

Argument passing is, or was, defined in the "argument association" section of the standard, which obviously doesn't preclude implementing by reference. I don't know whether the same language was in the '66 standard. It isn't anything to do with protected memory as far as I know (which is early '60s); I don't know what CDS is. The point of f2c was just to show that what happens with the invalid code depends on the backend code generation with essentially the same frontend. Regarding different sorts of argument passing, ALGOL 60 had call-by-value, -by-reference, and -by-name.