[rescue] 3.5" floppy drive question(s)

Curtis H. Wilbar Jr. rescue at hawkmountain.net
Sat Oct 11 14:06:18 CDT 2008

Curious George wrote:
> --- On Sat, 10/11/08, James Birdsall <jwb-tech at picarefy.com> wrote:
>> Curious George wrote:
>>> --- On Sat, 10/11/08, Curtis H. Wilbar Jr.
>> <rescue at hawkmountain.net>
>>>> Was wondering if 3.5" HD floppy drives can be jumpered/used in
>>>> a system that only supports 720K, using them as 720K only
>>>> drives ?
>>> AFAIK, if you cover up the hole in the medium that indicates
>>> the medium to be "HD", the drive will sense it as a 720K
>>> floppy and act accordingly.
>>> *However*, you will probably get less than ideal results this way.
>>> IIRC, the data track on a 720K drive is wider than the *head* on
>>> a HD drive.
>> That was true for 5.25" drives, where they added more tracks
>> (from 40 to 80) as well as more sectors (9 to 15). For 3.5"
>> drives, the number of tracks is constant (80) but they doubled
>> the number of sectors instead (9 to 18). The width of the head
>> could be different too, but there's no 
>> obvious reason why it should be. Everybody knew about the
>> problems using a 1.2M drive to make 360K disks, but I don't recall
>> hearing anything about similar problems with 1.44 and 720.
> Argh!  My bad  :<  I use DSHD media in my Unisite with the
> above trick -- but, as a matter of habit, always bulk erase
> *any* media before repurposing it.  (So, if there *are*
> problems, I'm immune).

There isn't an oersted difference between HD and DD 3.5"
media ?  Or is it not a large enough difference to prevent
HD on DD and DD on HD from working correctly ?  (I have
a bunch of 3.5" disks around I formatted 1.4M back in the PS/2
days.... have never tried to read them since then, I'm guessing
I'd have to fake out the sensor in order to read them on a
regular PC/drive, right ?... or for read it doesn't matter ?)

-- Curt

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