Ah, good old FDFORMAT
Not forgetting the TSR that went with it, FDREAD ;-)
Normal DD format 9 sectors/80 tracks would give 720K. An Atari ST disk typically had 10 sectors/82 tracks, giving 820K for not much effort. An Amiga could shoehorn 1.1Mb onto the same disk.
And +1 for 5 1/4's being amazingly robust. I once had some posted to me, where the postie had folded them in half to get the envelope through the letterbox. They still worked.