We were given an expensive device (X-ray fluorescence
analyzer) that had a dying computer. The instrument had an
ISA bus card to interface to it. I cloned the hard drive,
and tried to get it to boot properly on a new "industrial"
computer that had ISA slots. The original OS was DOS 3.1
That didn't work well, so we got a DOS 7.1 install disk, and
had to do a bunch of magic to get the ANSI graphics support
loaded properly, but then the whole thing worked!
I have a Samsung-built pick and place machine at home that
runs Windows 95, because the user-mode control program talks
directly to the hardware (a Motorola 68040 VME board
connected through a dual-port memory).
So, both of these systems require ANCIENT OS versions.
Jon