Unless we're talking about ancient hardware terminals, the computer sees the actual raw scancodes coming from the keyboard. Control (whether by itself or in combination with something else) is no different than any other key. It's the software that maps those combinations to ASCII control characters, which is why this works the way you described on most Unices (where, if I remember correctly, it's the tty that is doing the mapping) but not e.g. on DOS/Windows.