MIDI data maybe stored as .mid file for computer use. Multi-track sequencer will store the instructions in a project to be used, this can be hardware based or the sequencer might be a software program, for later use.

The .mid file format stores MIDI data as all tracks combined or individual tracks. This is done by recording the MIDI data sent from the controller (instrument). A sequencer that can use MIDI can then be used to reproduce the performance, keeping the tempo and effects of the original performance. The data is organized into chunks, a header chunk (format, tracks and timing) and track chunk (events).

MIDI data transfers from a controller to another device or software application (software synthesizer or Sequencer) as a 10-bit serial data stream (1 byte MIDI data and 1 bit each for Start and Stop data), at a bit rate of 31.25 kilobaud (kilobaud gate changes).

The MIDI channel message consists of the status byte followed by the data bytes. Status bytes are Note on Note OFF, while the data byte specifies the note pressed and the velocity of that press.
MIDI message signals represent:
 Note-on: start playing
 Note-off: stop playing
 Program Change: switch to a different channel (instrument)
 Pitch Bend: change pitch of note in accordance to the pitch bend wheel
 Control Change: the application of effects on instruments
Etc.

Control Change messages. Switch controllers and variable controllers (there 128 possible control parameters 0 is a possible state as well). Switch controllers turn a device on or off. The variable controller can change the parameters.

Continuous Control  information includes pitch, tempo, panning, key signature, volume, time signature, modulation, reverb, chorus and program change messages.

A MIDI Control Change message is a status byte followed by the data bytes. The status byte will be Effect ON or Effect OFF, while the data bytes may specify the continuous change in the parameters of the effect.

Pitch values range 0 to 127 in General MIDI. Changes in the pitch wheel make one semitone change in pitch. This change is represented by a sequence of Continuous Control data bytes.

Every instrument may have a channel. With 16 channels it is possible to have 16 MIDI events or channel messages all through the same, MIDI cable. Program Change message indicates which of the 1 to 128 (GM) instruments, voices, timbres, etc., that is chosen.

SysEx. MIDI data contains information about the parameters of a device in the signal chain. Those specific parameters of the device's function used to process data during a performance are then controlled through the SysEx number assigned to it. The transfer of the data involving the parameters of the device is called the SysEx dump. The device has an ID number which allows messages to be directed to individual devices. This allows the interchange of sound synthesis parameters. From specific devices to and from the computer.

Midi file editing is easier due to the sequential nature of recording you can access the individual action or insert etc. With other forms of music storage it is considerable harder.

Midi has two standards (SMF). Midi type 0 involves one track of data. Midi type 1 has more than one track of data.

MIDI Clock transfers data on song position pointers and the tempo rate. It facilitates MIDI device synchronization.

MIDI Time Code (MTC) is a reference point a MIDI performance. The code standard is based on frames, seconds, minutes and hours (hours:minutes:seconds:frames:subframes when displayed). MIDI Time code can be synchronized to SMPTE Time Code and transfer SMPTE data in MIDI format.

MIDI Machine Code (MMC) will allow Master, without synchronization, control of another device (start and stop).

There are many differing forms of midi devices which you use is dependant on the type of musician that you are. They can all be used for hip hop where anything goes.
Midi Keyboards, Wind Controllers, Pressure Pads, Pedal Boards.

Pedal boards can be used for playing bass lines, or can be used to help arrange music if connected properly to other midi devices. They normally contain velocity sensitive pedals. Offering control over Program, Bank, Channel, and Transposition. Manufacturers include Hammond and StudioLogic.
In 1970s Peterson developed and began manufacturing electronic carillon systems for the I.T. Verdin Company, and the tuner product line was expanded with new specialty models for schools and performing musicians. Also introduced at this point were the "Bottom Line" pedal bass unit featuring a unique pedal keyboard. The birth of pedal boards stems from organ use.

These are pads that are ergonomically designed for percussists to enact midi control events. Conceptually ideal for the hip hop beat maker.
Expressive percussion and drum parts the made possible with velocity-sensitive pads for playing the drum sounds in software, It can also be used to control events launching loops and samples. Velocity sensitivity makes it possible for MIDI control.
Manufactures include Akai and M audio.
Touch sensitivity in the use of midi systems was ultimately pushed by Korg. This form of midi development, initial a commercial slow endeavour, the concept was based largely on synthkit and oasys

These are responsive wind and lip sensors. Sometimes they use a reed or recorder type mouthpieces, with a variety of fingering modes.
It converts fingering/breath control etc. into MIDI output that is used to control MIDI synths. Normally based on a soprano saxophone, but other instruments are available.
The most common are the Yamaha WX series and the Akai EWI series.
Synthophones are saxophone bodies with midi output. The basic concept that was to give birth to the Electronic Valve Instrument began in 1964. Nyle Steiner, a trumpeter, music student, and engineering employee at an electronics firm, envisioned an electronic string instrument in which the string fingerings could be manipulated utilizing trumpet-fingering technique. Overtones were a problem when manufacturing wind controllers. These problems were overcome by, the original Lyricon which was a wind controller, it that drove a computer that generated overtones. There were 3 Lyricons manufactured by Computone, Inc., in the 1970's.

These were some of the first midi devices and they have dictated the features of all devices due to their wide availability. Manufactures include Yamaha/Akai/Roland etc. The ergonomics of their design differs immensely some attempting to look like guitars but most are similar to pianos. They are born form early synthetic keyboards
Most midi keyboards encompass features such as modulation, velocity sensitive keys, pitch benders and after touch control.