It is software (grandorgue) that pretends to be a pipe organ (the instrument). In order to run fast enough it needs to load every sound sample into memory to play, as well as usually multiple kinds of sound endings. I play professionally on a “small to mid sized” pipe organ with 1,438 pipes. The one I load for use at home has more than that!
The instrument was from the 1960s and I rebuilt it with a pi pico that you can see here, and you can hear the before (analog sound cards) versus one of the organs I’ve loaded into it here.