This belongs on a sound card for some reason!! :D

I can tell that this particular port is more or less from the same time as the PS2 ports in the post's photo because of the color. The standardization of this port happened long before the standardization of colors to indicate the capabilities of said port. We mostly only see this in variously capable USB ports today. If I remember correctly this yellow color would have been used for a joystick or controller of some kind, but there may have been other ports with the same shape and pin configuration that would have different purposes.