Re: But does the BIOS and DOS see it as a floppy?
I used to have a non-standard format utility which would create (for example) an 800K floppy by formatting with an extra sector (*). On some PCs these discs were fine as standard, others needed a small TSR to read them.
Later versions of MS-DOS actually allowed the creation of these discs without a special utility, if command line arguments were used to specify the sector count.
(*) more than one extra sector or additional tracks were also possible, but reliability went down as sectors went up. Extra tracks was dependent on the drive being able to move the heads far enough.