Midi overview
  Think of midi as a player Piano, the information on the large spool that turns relays exactly what the musician was playing right onto a real piano not a recording, this means that no emotion is lost, and no sound quality is lost. It is these kinds of information and emotions that Midi can be used for today.   . Midi information can be recorded and then directed to a chain of equipment to create a full orchestra if you’d like with all sorts of keyboards and sound producing equipment                                                  .

                                                           Quick history
   , Even though electronics such as keyboards, sound modules, keytars, and saxophones were produced when midi standards where still being determined. Most all the basic function of Midi should work fine with even today’s Midi electronics. The Basic midi standards were established in the early eighties, and to this day are called General Midi. The MIDI Manufacturers Association also known as (MMA) was Born.  Electronic companies such as Yamaha, Roland, and Casio all had a large roll in how we see midi information notated and transposed today. Today’s Midi information can relay information such has how hard or how soft you hit the keys on a keyboard, send movements made on a mixing board, as well as much simpler things like be used to assign a priority level in a chain of equipment with midi. This information can be recorded to a Midi recorder and that played back.
                   

                                      Basic keyboard MIDI IN and OUT

                                         
                                           Keyboards with midi out

What sometimes is referred to as a controller keyboard indicates it has a midi out, the ability to transmit midi data.
                                              

                                           Keyboards with MIDI in
 In order for a keyboard to receive midi information it must be able to act as a slave meaning in has a Midi in port 
  
There is a ton of information on midi and how its works. If you like keyboards and want to know more on how to link together keyboards, Hard disk recorders, computers, and more with Midi, There are some great sites out there.
basic midi