MIDI stands for Musical Instrument Digital Interface and is a means by which your PC can communicate with musical instruments and devices.
All PC's come with a synthesizer or the capacity to add one via a sound card. Nominally,the PC synthesizer will have 128 sounds which will conform to the General Midi format. For both your soundcard synthesizer and external MIDI devices you will need drivers. You can check whether the required drivers are installed by going to CONTROL PANEL and clicking the MULTIMEDIA Icon [Win9x] or SOUNDS AND AUDIO [XP]. The Tabs for Audio and MIDI will indicate whether the drivers are installed.
If there are drivers then the list should contain something indicating MIDI synth and MIDI out. Sometimes if your synthesizer is a WAVETABLE type then you may see other options. The Audio tab should show drop down lists for Record and Playback. If any of the above are missing you will experience problems with sound playback and recording and MIDI functionality.
Installation of these drivers should happen when your soundcard is installed,but this may not supply you with MIDI functionality,in which case you will need to find a compatible driver for your sound system or use a generic one such as the MPU-401 which is generally available on the internet.
If using XP+ then you may need a USB adaptor or an interface that connects to USB.
If using Win9X then the connection from the PC to your external device will be via a D-type plug to two 5 way DIN plugs. The necessary cable is available in PC shops and on Ebay.In order to run a MIDI system files called .mid can be played from Media Player,but to record your own synthesizer recordings you will need Cakewalk,Sibelius,Orchestra Plus or some other sequencer software. Most of these allow some sort of visual feedback both of musical notes and staves and also bars and sometimes a piano-roll display and occasionally a mixer.
Some modern keyboards support "MIDI exclusive dumping" which allows the memory contents of the keyboard to be passed to the PC for storage or allows control of parameters which are not on the front panel. This feature uses the System Exclusive (.syx) Code of MIDI and to exploit it you may need something like MIDI-ox installed which monitors all MIDI data, edits it and also allows SYSx data storage.
Note also that software such as Winamp will play .mid files as well as .mp3 audio files. .mid files are not audio files as such,but a list of triggers sent to the sound card telling it how to play back music.The exact coding of these triggers can be found in the SEE ALSO section below.
The end result is that your PC either plays it's internal synthesizer and/or external ones,as many synthesizer components can be chained together and be orchestrated by the PC. Input can be given by a keyboard or other instruments and the PC will record everything that happens showing the collected data in various ways,maybe as musical notation or as lists of MIDI commands. Editing can then take place,and if you happen to have played a bum note,it can be removed. MIDI sequencers typically can play 16-32 tracks and so you have a whole recording studio on your PC.Some sequencers also support the addition and use of .wav files and so you can record audio into your musical piece from live instruments too.
You may find that such programs produce their own file format which maybe peculiar to that program [Cakewalk uses .wrk for example] but all should support the MIDI standard .mid file.
It may also be the case that sequencer programs will support plug-ins to allow additional functionality,such as being able to read a score direct from manuscript paper in essence OCR-ing music.
See Also: First a word about MIDI,Sweet Sweet Music,MIDI-ox,Cakewalk,Orchestra Plus,Sibelius,Cubasis ,Finale, Garritan,Reason,MIDI Concepts,More about MIDI,Winamp ,Music Technology-MIDIFILES,Practically MIDI,System Exclusive,MIDI Tutorials,Music and Computers