MOD format
The Amiga's module format — samples and note patterns in one file, so the tune played on the machine instead of being streamed.
A MOD file (module) bundles a handful of digital samples with a grid of note patterns that say when, how loud and in which channel each sample plays. The format was born with Karsten Obarski's Ultimate Soundtracker on the Amiga in 1987 and drove the machine's four sound channels directly. Because both instruments and score lived in the file, a MOD sounded the same everywhere — unlike MIDI.
Its small size made MOD the natural music carrier for the demoscene and the BBS world, and it became a de facto standard that later grew to four-digit channel counts through successors XM, S3M and IT. ProTracker became the tool that defined its sound.