for the trs80, there were 35 track floppy drives and the (ohh, cool) 40 track drives. I think it was 80MB per side and generally only used one side of theh floppy.
we called drives that could write to both sides 'flippy'. you would eject the floppy, fip it over and reinsert it. you'd often get sector errors, as the 2nd side of the floppy disk was the 'reject' side, from the vendor. best side goes the 'normal' way. but we could often get use out of the 2nd side. rarely were there drives that used dual heads, so the usual thing was to write to the first side, wait for it to fill up, then eject and try writing to the 2nd side.
you would also have to punch a hole (the write-protect tab) in the other side of the floppy so that you could control read/write off each side. a tape was placed over the hole to allow writes; removing the tape made the floppy write-protected.
I think there was a max of 4 floppies you could chain. the filespec was "file.txt:drive", eg "file.txt:0" or "file.txt:1" for floppy 0 (first one) or floppy 1 (2nd one).
sigh. fun times. 48k should be enough for anyone.