Microsoft developed its bus mouse card with its InPort chip and Logitech developed its own bus mouse card that was comaptible with the Microsoft mouse. They were installed in an 8-bit ISA expansion slot inside the computer. Using the mouse port freed up the serial port for other peripherals. The mouse contained no microprocessor, rather, logic on the card registerd mouse events. Microsoft standardized to the D-ring and 9-pin round bus mouse plug which inserts into the 9-hole bus port.
The Logitech Bus Mouse bus board came in two types of connectors: DE-9 socket connector and the 9-pin Mini-DIN Connector, round with a bar on one side (pictured).
Logitech (C)1987 bus mouse card (left) and a later Microsoft In-Port™ (c)1986-1989 (right) mouse bus card, considerably downsized.
Apple developed its own mouse card, the Apple Desktop Bus. The ADB plug is configured as a 4 pin mini-DIN connector.
Apple Desktop Bus (ADB) mouse pinout diagram courtesy of user Mobius at Wikipedia.