It uses a MIDI-based system for storing events, and the most recent versions save music in MWK files, similar to Standard MIDI Files with additional text and symbol events.
In addition, the Songwriter edition allows the user to create drum notation, and customize chords and fonts.
Unlike their modern counterparts which share a common "MWK" proprietary format for saving data, the original MW/MWP saved in a different and now obsolete PBL format (.pbl extension).
As these programs are not compatible with Windows 2000 or later, and the current editions do not support PBL, users may find they are unable to open legacy scores created with MW / MWP.
A third party online converter exists [1], but is not formally recognized by Voyetra and is somewhat incomplete.