With the Mac SE and II, the switched to ADB, which looked like a PS/2 port, but you could daisy chain your mouse, keyboard, and other inputs like tablets or joysticks all into one jack in the back of the computer.

The port looks similar - both are mini-DIN - but ADB has four pins while PS/2 has six.

ADB was first introduced in 1986 on the Apple IIgs, and later was used in all Macs from the SE until the iMac. For the first few years there were two ADB ports, but in 1990 (maybe starting with the Mac IIsi?) they reduced it to one and started shipping keyboards with ports to daisy chain the mouse from.