When USB 1.0 launched, one of the ports it aimed to replace were PS/2 ports. Mice and keyboard had mechanically identical PS/2 plugs but would not work if plugged into the wrong one. Even worse ...

There was a time when if you bought a USB mouse ... you bought a mouse with a PS/2 connector fitted, it may well have come with an adapter for a 9-pin RS232 serial port. Those mice from a decade ...