The only major consumer-level use of single-sided 3.5" diskettes were by Apple (in the original Macintosh) and early models of Atari 520ST.
I've got a big box of formatted, blank (empty) single-sided double density 3.5" floppy disks in our garage. From what Dad said a few years ago, they're not Atari disks (though he did work at Metacomco in the early Atari ST days) but came from something later, either PC related or some 68k based system (probably a UNIX type one).
All blank, unlabeled disks packed in rows in a brown cardboard box with a cardboard spacer in the middle. (they look unused to me, just slightly loose and disorganized in the box from some being taken out previously)
They also seem to format OK to 720k DS disks, but I haven't torture tested them. It will not format them to 1.44MB DSHD disks, throwing error messages when I attempted it.
(given single-sided 5.25" disks often work as flippies or double-sided disks, I doubt there's much/any difference with SS disks other than formatting and maybe quality control: it was the single-sided drive mechanism that was significant: being cheaper, available earlier, and potentially more reliable or easier to harden for critical reliability: like specialized mainframe or military applications)
I know Atari started off with single-sided drives simply for the cost saving measure. (and as they were competing with Apple, who was using 400kB single-sided 3.5" disk formats for the Macintosh)
Windows 98 seems to recognize them as 720k DSDD disks with 366 kB free, but the format used can't be read or written to by DOS/windows. (either due to only one side being formatted or due to it being an incompatible partition format ... maybe DOS or CP/M like but big endian format data, like Atari TOS does: I'm not sure how typical 68k UNIX disks are formatted)
They're stored right next to a box full of Mizar/Integrated Solutions documentation with manual for a DEC 68k20 VME bus system. (and I remember dad had a big rack mount server/minicomputer like system set up around 1993 in the garage, I think it was surplus hardware he'd had in storage from several years prior, and he'd left Mizar around 1990, I believe so it probably got surplussed then)
So that style of disk might have been more common in specialized market sectors in the mid 1980s. I'll need to check the date on that manual in the garage, but I believe it's similar to this system:
http://bitsavers.informatik.uni-stuttgart.de/ … inary_Jan86.pdf
Edit: some disks do seem to have MS DOS readable data/formatting on them, and 720k DSDD formatted (or a format close enough to MS DOS files to read, even if the files might be interpreted incorrectly). I did notice some of the disks had write protection slots switched open but didn't think much of that initially, and most do appear to be unreadable or unformatted. (some may be single-side formatted and unable to be read properly) So maybe they were a mix of unused and discarded/surplus disks.
I'll have to set the ones with intact data aside and see if they are actually Atari TOS format disks or not. (or maybe Xenix formatted disks, though I think all of Dad's own 68k based Xenix systems were 8" and 5.25" based ones, SCSI drives aside ... maybe he ran the x86 version of Xenis at some point, too)
And I know the TOS (68k GEMDOS) has a very similar filesystem and disk format to DR-DOS and MS/PC-DOS, though not directly compatible. (close enough to make translation software relatively simple on the ST) Though I've never seen what happens if you try to read a TOS disk as if it were MSDOS formatted.