It is interesting to note that the drives used by
Radio Shack had another
"feature" in that they connected a "drive selected" line on the Data
connector.
IIRC, ST412 drives are supposed to do that too. Not many controllers
bother to look at that signal, but I've come across at least one that
does (and thus it doesn't matter which order you plug the data cables in.
I'm got a vague idea tha DMD did this too.
-tony