Henk Gooijen wrote about the RX50:
Another "quirk" of the RX50 is that the head
movement stuff is also
shared for both heads. So floppy-to-floppy copy can be slow because
the head has to reposition every time the access goes from one disk
to the other.
If you are doing a file copy, it can be inefficient. But it's
optimal
for track-at-a-time disk image copy, because for each track you only
have to position once, read the track from the source drive, and write
to the destination drive.