My heathkit H-89, which used SSHS mounted vertically, had a note in the
manual that using "flippy" diskettes was not recommended, as dirt and
suchlike (which collects on the liner during normal operation) was likely
to fall out if the disk were flipped, and thus run backwards.
S'pose that was so they could sell you more disks, or was there some truth
to that?
I can think of very few home units which had vertically mounted drives...
Trash-80's are all that come to mind.
P Manney
"Flippy": The second side can often be used
in a single sided drive by
flipping the disk over. In the case of Apple ][ and Commodore, it
requires punching a write enable notch. (Which does NOT need to be square.)
On TRS-80, IBM, etc, it is necessary to also punch an additional
(symmetric) access hole for the index hole. (jigs for marking and
punching used to be available.)