MIDI is a set of hardware and software protocols used by electronic musical instruments to communicate. It was first released in 1982 and has become the de-facto communication standard between electronic musical instruments. The protocol specifies the physical hardware parameters for the cable and interfaces, and provides a well defined set of communication protocols to exchange musical and timing data.
Prior to MIDI there were several analog, and later basic digital, connection protocols. The earliest, circa. 1974, would transmit note information as a voltage though a wire from one keyboard to another. Later, 1980 - 1981, Roland created a basic digital protocol, DCB. The MIDI Manufacturers Association (MMA), working with the equipment manufacturers, defined a standard protocol and physical connection which allowed equipment from all complying manufacturers to connect and communicate with each other.
>From 1985 MIDI interfaces started to appear on home computers and soon after sequencing programs appeared.