How do you make sure you support all the possible devices that will request a page from your server? If you divide between desktop and mobile, what do you serve

How do you make sure you support all the possible devices that will request a page from your server? If you divide between desktop and mobile, what do you serve a tablet? If you make a tablet layout, what do you do if it changes orientation? Once you added the tablet, what do you serve a web-enabled TV? A handheld console? A high-resolution display? Responsive is about responding to container characteristics, instead of relying on the assumption that a certain known device has certain characteristics. Even with responsive, the rabbit hole goes waaay down, but at least you're avoiding the ghetto effect of "supporting" a set list of circumstances.