Also the PS/2 keyboard and mouse connectors. Before that mice were speaking to serial ports or required an add in card with a nonstandard port. the people buying PS/2's were often very concerned with mice, they'd seen them on TV and they wanted one.
Same physical port. Perfect for plugging into each other and having neither one work. Later on they color coded them (purple and green, some companies used orange?)
I was always jealous of the Mac's ADB. You could daisy chain it, plug any device into any port, it was nice.
I think there was nothing more standard than RS232. You needed to add a "multi" board (joystick, parallel, rs232), yes, but that was absolutely standard.
"Bus" mice were popular too. [0] Cheaper to produce than RS2323 mice I think, but required the special interface card or motherboard support.
The bus mice were semi-popular with Amiga owners because they were easily converted to Amigas. RS232 mice could be used with Amigas too, but only worked in Workbench programs which used the operating system drivers. Most Amiga games etc used the mouse hardware registers and the RS232 mouse would be ignored then.
