Abbreviation for Digi System Init. Init is a fancy word for Extension on the Macintosh – historically the extensions that load upon boot up were called inits, which is short for initialize. These days we just call them extensions, but DSI is an old abbreviation. The DSI is, therefore, an extension that must be loaded by the computer in order for it to be able to “see” any Digidesign hardware that may be installed in it. It works in conjunction with DAE to enable recording with Digidesign systems.