I thought you could use 3.5" HD/DD disks in a
DS/DD drive just fine. At
worst a piece of tape over the "wrong" hole if necessary.
Not if you value your data (and I do -- what's the point in writing
something to disk if you don't intend to read it back again?).
The coercivity of the media _is_ different between the DD and HD 3.5"
disks. Not very different, but different enough that you _will_ have
reliabilty problems.
-tony