The three major computing platforms, PCs, Macintosh, and Unix workstations, had three different audio file formats. These files are similar to digital audio tape. That is the entire sound is captured as a wave form.
Files can get quite large.
In the pre-web days it was common to need to translate among the three formats. This often involved invoking Unix commands with all kinds of arcane text switches. Thankfully things are much easier now. Most audio players can read more than one format. MIDI is different that recording the actual sound.