And if you were to go back a few more years into the past, you’d have found when 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.

DB (D-Sub) Connectors and COM Ports A serial port on a PC is a male 9-pin connector (DE-9 D-sub). Early PCs had two 9-pin connectors or one 9-pin and one 25-pin (DB-25). On a PC, serial ports are ...