There can be remarkable differences in the sound produced by a MIDI file, depending on the machine on which it is played. MIDI files traditionally only contain instructions that trigger sounds played by a synthesizer. On a personal computer these are commonly sampled sounds contained in a computer's sound card.
The following problems might occur when playing MIDI files:
MIDI files encoded with a more recent version of the MIDI standard might not be correctly rendered if your machine doesn't support that version of the standard.
Some hardware manufacturers produced proprietary extensions to the general MIDI standard, not rendered by all MIDI players. Such hardware-specific extensions are to be avoided for MIDI files uploaded to Wikipedia.
The machine on which you play the file must have both the software and hardware enabled to play MIDI files. Digital audio players might play MP3 and most other standard audio formats but will not play MIDI files.
Free software is available to display the content of the most current types of MIDI files in sheet music and/or sequencer format, for example Rosegarden and Lilypond.
If your sound card does not support MIDI, TiMidity is able to play these files, or convert them to other sound formats.