MPU-401

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The MPU-401 (MIDI Processing Unit) is an old, now obsolete way to connect MIDI gear to a personal computer. It was designed by Roland, the company that helped create MIDI, and first appeared around 1984 as an external box with MIDI IN, MIDI OUT, MIDI THRU, TAPE IN/OUT, MIDI SYNC, and a slot for an interface kit that plugged into a computer.

Over time Roland moved most of the electronics onto the interface card itself, shrinking or removing the breakout box. By the late 1980s other companies made MPU-401 compatible boards, some using Roland chips and others reverse-engineering ROMs (such as Voyetra and Midiman/Music Quest). Hobbyists even cloned cards like the Music Quest PC MIDI Card 8BIT, and later a version added a wavetable header similar to the Roland MPU-401AT.

The MPU-401 can run in two modes: intelligent (normal) mode and UART mode. In intelligent mode it offered features like an 8-track sequencer, MIDI clock output, SYNC 24, Tape Sync, and a metronome. In UART mode it simply relays MIDI data between the PC and devices. As computers grew more powerful, the software side could handle these tasks, so UART mode became the standard. Early UART cards were still advertised as MPU-401 compatible.

In the 2010s, hobbyists created SoftMPU, a software layer that upgrades UART boards to act like intelligent MPU-401 hardware—but it only works on MS-DOS and isn’t compatible with all games. Later, a hardware board called HardMPU placed the intelligent logic on the card itself, but it currently supports playback only (not recording).

Today USB is common for MIDI, and USB-to-MIDI adapters let modern gear work with older DIN connectors. Windows dropped MPU-401 support in Vista, but a driver remains available via Windows Update. Linux and macOS have continued to support MPU-401-era interfaces.