MIDI stands for Musical Instruments Digital Interface. It is a cross-platform standard for interfacing musical instruments to a computer, and for playing music through a musical synthesizer such as that found on a computer sound card.
To play midi files, you need appropriate software (such as the Media Player in Microsoft Windows), a sound card (some computers, such as the Macintosh, have this capability built in), and stereo speakers. On an IBM compatible PC, you need as a minimum a 16- bit sound card. Although you can play some midi files on the old 8-bit sound cards, the results are not satisfactory.
You will get VERY SIGNIFICANTLY SUPERIOR SOUND with a "wavetable" sound card. With a standard sound card, the music will be satisfactory, but will definitely sound like it is coming from a synthesizer. With a wavetable card, it sounds like you are listening to the real thing.
Updated 1 Dec 1996