need 720k 3 1/2" disks

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Tue Jun 10 19:13:30 2003

> > > I I need a couple 3 1/2" diskette for an old 8086 six laptop too boot
> On Mon, 9 Jun 2003, Stuart Johnson wrote:
> > Have you tried using a HD floppy and putting tape over BOTH sides of the
> > hole that marks the disk as HD? I should think that you could then format
> > the floppy as a 720 easily. I haven't tried this myself, but "Logic is the
> > art of going wrong - with confidence". I write enable factory-made read-only
> > 1.44 floppies in this manner, and I use ordinary frosted "scotch" tape with
> > great success.
>
> 1) Many drives use a light and photocell to sense that hole. At least use
> an opaque tape!

Strangly, every 3.5" drive I've worked on (and I've taken quite a few
apart for repairs) have mechanical sensors. Either switches, or
mechanincal 'flags' that work with slottted opto-switches. In the latter
case, of coursem the light beam goes nowhere near the hole.

I don't doubt that drives using optical sensors exist, but I can't think
of one at the moment.

>
> 2) Many 720K drives have no sensor for the "media ID" hole, so tape, etc
> might turn out to be unnecessary unless/until you try to transfer files by
> putting that diskette into your 1.4M drive. However, there were some
> drives (THANKS, Tony!) that use that same location for the "is there a
> disk in the drive" sensor.

Yes. The old Sony drives (used in the HP9121, to tie in another thread)
have the disk-inserted sensor (which is a flag + slotted optoswitch in
this unit) in exactly the same position as the HD hole. These drives will
not recognise that an unmodified HD disk has been inserted.

-tony
Received on Tue Jun 10 2003 - 19:13:30 BST