[Coco] 720k 3.5" floppies

Joel Ewy jcewy at swbell.net
Sun Nov 4 17:44:56 EST 2007

Gene Heskett wrote:
> On Sunday 04 November 2007, Bruce W. Calkins wrote:
>> ----- Original Message -----
>> From: "Derek" <dml_68 at yahoo.com>
>>> If you put something over the hole on the upper left side
>>> of the 1.44 MB floppy disk you will have better luck.
>> That is precisely what I did.  1.44M media is different than 720k media.
> It (the HD diskette coating) is about twice as hard magneticly, and the 720 
> drives don't have enough write power to fully magnetize the coating.  
The question I've always had WRT this is "how does a 1.44M drive treat
media it identifies as 720K differently from media it identifies as
1.44M, other than expected bit density (how fast it reads/writes the
disk)?"  It stands to reason that using a high density disk as a faux
low density disk might not work well when you're trying to write (or
possibly read) it in a low density drive.  But the high density drives
have exactly the same interface as the low density drives.  I've used
1.44M drives as 720K drives on the CoCo for years -- with actual 720K
disks.  Does the presence of the HD hole in the disk alter alter the
write current of the disk heads, or does it just signal the disk
controller to jump up to the higher data rate?  If only the latter, then
it should be possible to use HD disks to stand in for low density disks
-- if you use only HD drives with them.  But if the HD sense hole
actually causes the drive to 'pump up the volume' then I could see why
this wouldn't work.


> It may 
> be something that could be adjusted, if one had the actual schematics, 
> something the chinese aren't supplying with anything newer than about 15 
> years ago.
> Often you get a disk you can read just fine when its made, but two weeks later 
> its faded back into the noise.
>> Bruce W.
>> --
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