From danforcz@yahoo.com Fri Aug 21 06:28:32 2015
Subject:Re: Roland VK-1 - Hammond on separate output?

You are right, there are some issues in the early MIDI world, that's
the reason why some low numbered MIDI controllers are not used because
different firms used them for different purpose.

MPU-401 for one of the first MIDI interfaces for PC, it became
standard. Depending on the model you have it's can be still usable,
also with Mac OS and Linux...

Daniel Forro