USB MIDI
The USB device class for MIDI, which lets a keyboard or synth plug in without its own driver and has replaced the five-pin DIN cable on most gear.
The USB-IF published the MIDI device class definition in 1999 as a subclass of USB Audio Class. Each MIDI message is wrapped in a 32-bit packet whose first byte names a virtual cable, so one USB lead can carry up to 16 independent MIDI ports of 16 channels each. It runs many times faster than the old serial link's 31.25 kbit/s, and class-compliant devices work out of the box on macOS, Linux and Windows.
The snag is USB's asymmetry. Classic MIDI connects two instruments directly, but two USB devices need a host between them, usually a computer. That's why DIN sockets are still on so much hardware. A revised spec for MIDI 2.0 arrived in 2020.