Albert de Boer tried without any success to find a laptop computer
that has a MIDI-out port to feed electronic files to his PowerRoll
(MMD 2000.03.22.11).  I am going to face the same problem with my organ
project and have deposited an old DOS operated type PC-AT laptop on my
shelf for the purpose.

Just to play an extant file (as opposed to edit it in a modern manner),
in hardware you need no more than that plus an adapter between the
computer serial port, 25- or 9-pin D-sub connector, and the MIDI 5
socket DIN connector.  MIDI uses conventional serial communication
ports.  Historically it emerged with the early Macintosh computers
which as a by-product defined the odd 31.25 kHz MIDI clock rate.

The problem is rather with the software side.  To execute, what you
need is a sequencer program to read and interpret the MIDI file and
send its events at the proper times.  As I see it the missing link is
only a driver to set up the proper clock rate in the serial chip and to
handle the communication.  It used to be fairly straightforward to
write such a thing in the old DOS times, I guess much worse in, for
instance, a Windows environment.  No help to be expected from IBM or
Microsoft that want to sell their new products.

Anybody knows of existing such drivers?

Johan Liljencrants