MPU-401

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The MPU-401, where MPU stands for MIDI Processing Unit, is an important but now obsolete standard for MIDI interfaces for 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/IBM AT.
• 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.

The MPU-401N is an external interface, specifically designed for use with the NEC PC-98 series notebook computers. This breakout-box unit features a special COMPUTER IN port for direct connection to the computer's 110-pin expansion bus. METRONOME OUT connector was added. Released in Japan only.

Later, Roland would put most the electronics originally found in the breakout box onto the interface card itself, thus reducing the size of the breakout box. Products released in this manner:

• MPU-IPC: For the IBM PC/IBM XT/IBM AT and compatibles (8 bit ISA). It had a 25-pin female connector for the breakout box, even though only nine pins were used.
• MPU-IPC-T: For the IBM PC/IBM XT/IBM AT and compatibles (8 bit ISA). The MIDI SYNC connector was removed from this Taiwanese-manufactured model, and the previously hardcoded I/O address and IRQ could be set to different values with jumpers.
• MPU-IMC: For the IBM PS/2's Micro Channel Architecture bus. In earlier models both I/O address and IRQ were hardcoded, in later models the IRQ could be set with a jumper. It had a 9-pin female connector for the breakout box.
• S-MPU/AT (Super MPU): For the IBM AT and compatibles (16 bit ISA). It had a Mini-DIN female connector for the breakout box. The MIDI SYNC, TAPE ON, TAPE OUT, METRONOME OUT connectors was removed, but a second MIDI IN connector was added.
• S-MPU-IIAT (Super MPU II): For the IBM or compatible Plug and Play PC's (16 bit ISA). It had a Mini-DIN female connector for the breakout box with only one MIDI In and one MIDI Out connectors.

• LAPC-I: For the IBM PC and compatibles. Includes the Roland CM-32L sound source. A breakout box for this card, the MCB-1, was sold separately.

• LAPC-N: For the NEC PC-98. Includes the Roland CM-32L sound source.

• RAP-10: For the IBM AT and compatibles (16 bit ISA). General midi sound source only. MPU-401 UART mode only. A breakout box for this card, the MCB-10, was sold separately.

• SCP-55: For the IBM and compatible laptops (PCMCIA). Includes the Roland SC-55 sound source. A breakout box for this card, the MCB-3, was sold separately.

Still later, Roland would get rid of the breakout box completely and put all connectors on the back of the interface card itself. Products released in this manner:

• MPU-APL: For the Apple II series. Single-card combination of the MIF-APL interface and MPU-401, featuring MIDI IN, OUT, and SYNC connectors.
• MPU-401/AT: For IBM AT and compatibles. Includes a connector for Wavetable daughterboards.
• MPU-PC98: For the NEC PC-98.
• MPU-PC98II: For the NEC PC-98.
• S-MPU/PC (Super MPU PC-98): For the NEC PC-98.
• S-MPU/2N (Super MPU II N): For the NEC PC-98.
• SCC-1: For the IBM PC and compatibles. Includes the Roland SC-55 sound source.

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.

With computers becoming more powerful, the features offered in "intelligent mode" have become obsolete, as implementing them in the host system's software became more efficient. As a result, the UART mode became the dominant mode of operation, with many clones not supporting the "intelligent mode" at all.

The current trend in MIDI world is to use 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. MPU401 support is no longer included in Windows Vista.