2. PS/2 connectors
IBM introduced this mouse and keyboard connector in 1987 with its line of PS/2 personal computers (in a failed attempt to recapture its dominance of the PC market).
Since the ports were not designed to be hot-swappable, plugging a mouse or keyboard into a powered-up PS/2 port carries the risk of damaging your motherboard.
Today, most mice and keyboards connect via USB, so why are PS/2 ports still so common? Because some security-conscious companies disable the USB ports on their employees' computers so that the staff can’t smuggle out sensitive data on a USB thumbdrive.
I say make those corporate fat cats buy a special motherboard and save the vast majority of us some cash.