The MPU-401, where MPU stands for MIDI Processing Unit, is an important but now obsolete interface for connecting MIDI-equipped electronic music hardware to personal computers. It was designed by Roland Corporation, which also co-authored the MIDI standard.
Released around 1984, the original MPU-401 was an external breakout box providing MIDI IN/MIDI OUT/MIDI THRU/TAPE IN/TAPE OUT/MIDI SYNC connectors, for use with a separately-sold interface card/cartridge ("MPU-401 interface kit") inserted into a computer system.
- For this setup, the following "interface kits" were made:
- MIF-APL: For the Apple II.
- MIF-C64: For the Commodore 64.
- MIF-FM7: For the Fujitsu FM7.
- MIF-IPC: For the IBM PC/IBM XT. It turned out not to work reliably with 286 and faster processors. Early versions of the actual PCB had IF-MIDI/IBM as a silk screen.
- MIF-IPC-A: For the IBM AT, works with PC and XT as well.
- Xanadu MUSICOM IFM-PC: For the IBM PC / IBM XT / IBM AT. This was a third party MIDI card, incorporating the MIF-IPC(-A) and additional functionality that was coupled with the OEM Roland #MPU-401 BOB. It also had a mini audio jack on the PCB.
- MIF-MSX: For the MSX.
- MIF-PC8: For the NEC PC-88.
- MIF-PC98: For the NEC PC-98.
- MIF-X1: For the Sharp X1.
- MIF-V64: For the Commodore 64.
- In 2014 hobbyists built clones of the MIF-IPC-A card for PCs.
The MPU-401 can work in two modes, normal mode and UART mode. "Normal mode" would provide the host system with an 8-track sequencer, MIDI clock output, SYNC 24 signal output, Tape Sync and a metronome; as a result of these features, it is often called "intelligent mode". Compare this to UART mode, which reduces the MPU-401 to simply relaying in-/outcoming MIDI data bytes.
As computers became more powerful, the features offered in "intelligent mode" became obsolete, as implementing them in the host system's software became more efficient (than paying for dedicated hardware that will do them). As a result, the UART mode became the dominant mode of operation, with many clones not supporting the "intelligent mode" at all, being advertised as MPU-401 compatible.
In the mid 2010s a hobbyist platform software interface, SoftMPU, was written that upgrades UART (non intelligent) MPU-401 interfaces to intelligent MPU-401 interface.
In 2015 a PCB (HardMPU) was developed that incorporates SoftMPU as logic on hardware (so that the PC's CPU does not have to process intelligent MIDI).
Physical MIDI connections are increasingly replaced with the USB interface, and a USB to MIDI converter in order to drive musical peripherals which do not yet have their own USB ports. Often, peripherals are able to accept MIDI input through USB and route it to the traditional DIN connectors. While MPU-401 support is no longer included in Windows Vista, a driver is available on Windows Update. As of 2011 the interface was still supported by Linux and Mac OS X.