Quoting from the notes in that zip file:
"Note that most PC floppy controllers have broken single density modes.
Well, that's old hat to me. Around 1988 or so, I suddenly got problems
reading "elderly" 5.25" discs on new PC's. The reason was, that the
160K and
320K capacities were "designed out" of the floppy controllers normally used
in PC's
Since when have the MS-DOS 160K and 320K formats been 'single density'???
To me, single density disks use FM encoding, and the original IBM PC and
PC/XT controllers are strictly double-density (MFM) only devices (I have
read the schematics...)
Any PC floppy controller that can do the 360K format can also handle 160K,
180K, and 320K _in the hardware_. They're all much the same thing (and
are all MFM) . Of course your OS may not support such formats.
But very few PC floppy controllers (particularly single-chip ones)
correctly handle single-density (FM) operation.
-tony