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.

A mouse that plugs into the serial port on a PC. Serial mice used to be the most common type, but were replaced by mice that use the PS/2 and USB ports. Contrast with bus mouse. See mouse.

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.

Peer, L. A., in Transplantation of Tissues (edit. by Peer, L. A.), 2, 178 (Williams and Wilkins Co., Baltimore, 1959).

Serial ports are widely used by sensors for data acquisition, and they were standard on early computers for connecting a modem, mouse and other peripherals. Old Macs used the serial port for printers.