USB is modern but for lots of key input it is actually more of a hack in that it's not as good. I have gone into the reasons why plenty of times. PS/2 was designed for text input. It has a few drawbacks but all told and even though USB has far more bandwidth - it is NOT the best input device. There is probably a HID model that would be the best (and that could use USB) but the fact remains that a simple text only input is the easiest to work with and the easiest to split up and multicast.