Ah, the PS/2 ports—where mice and keyboards went to die before USB came along and made everything better. If you recognize these ancient circular connectors without Googling, congratulations! You're officially old enough to have debugged Y2K bugs and probably still have a drawer full of IDE cables "just in case." The blue one's for mice, the green one's for keyboards, and getting them mixed up was the original "USB superposition" before USB-C made us all flip connectors three times.
Remember the satisfying click when you finally got the pins aligned? And the sheer panic when you bent one? Good times. Kids these days will never know the joy of rebooting because you dared to unplug your keyboard.