Quoting Fred Cisin <cisin at xenosoft.com>:
The "official", "standardized"
support of 3.5" 720K in 3.20 was with use
of DRIVER.SYS and/or DRIVPARM. DRIVPARM was incompatible with IBM's BIOS,
and therefore was undocumented in PC-DOS.
Do you remember the details of the problem with DRIVPARM?
Mike