I would like to connect a 5"1/4 disk drive to a modern computer.

I haven't tried it, but this may do the job: Catweasel MK4plus PCI:
http://www.vesalia.de/e_catweaselmk4plus.htm?slc=us

Thank you very much : it looks like this is exactly what I was looking for.

Best regards,
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http://www.overbyte.be