Recent developments include on-board sound modules for locomotives as small as N scale.
The wind and lip pressure information is converted to MIDI data which is interpreted by the external sound module.
These were typically used to control external synthesizers, especially rackmounted sound modules as it was no longer necessary for each synthesizer to have its own keyboard.
Modular synthesizers used cables ("patch cords") to connect the different sound modules together.
Throughout the 1990s E-mu made many different sound modules along the lines of the Proteus series.
The functionality of the computer and I/O device plus the software is a superset of a traditional sound module.
Some guitar-synthesizers consist with two separated parts, guitar controller and interface & sound module, where the former control the latter (as in Roland instruments).
Yamaha also produced a smaller version of the S80, the S30, which contained the same sound module as the S80 in a 61-note keyboard.
In this case the 909 performs as a regular, 16-part multitimbral sound module, that happens to have a sequencer, too.
In essence, the 909 can be used as a very capable sound module without ever needing to fire up its sequencer.