[Coco] So, does anyone know where to get disk drives?

[Gene Heskett]

On Sunday 01 September 2013 23:05:03 Retro Canada did opine:

> only quad density drives using quad density medias can format in 720k.
> 
> this drive will format in 360k when jumpered to 300k

As a blanket statement, that's Pure Fooey.
 
The magnetic drive to the head ONLY changes when a QD disk is inserted in a 
QD drive.  The only physical difference is the width of the track in a 96 
tpi drive, is nominally 1/2 the width of the track that the 48 tpi (180k 
SS, 360k DS) drive uses.
 
I have worn out the heads on several of those drives.  From the Tandon 
100-4 to the Teac 55GFR,  and have never in 25 years been forced to use a 
QD marked disk in a 96 tpi 80 track "720k" drive.  Actually most will step 
in to the 83rd or 84th track, and will do 765K if the 84th track doesn't 
hit the spindle drive hub.

One such drive is in the drive tower behind the coco3 right now, but its 
connector currently has a 3.5" adapter in the card edge connector, plugged 
into a Mitsumi 3.5" drive.  With DD disks in it, the coco doesn't know the 
difference.

> On 2013-09-01, at 10:10 PM, Joel Ewy <jcewy at swbell.net> wrote:
> 
> On 08/29/2013 01:04 AM, Mike Pepe wrote:
> > (most) 1.2MB PC drives are useless- they spin at a different rate.
> > 
> > Aside from the complications of building the cable with the proper
> > twist and connectors, the 3.5" works great. In a pinch you can use
> > high density disks and cover up the HD hole, but I wouldn't trust it
> > with anything I cared about.
> > 
> > 
> > ...[snip]
> 
> I do have a number of Teac FD-55GFR drives, which are 1.2M 5.25" drives
> that can be jumpered for a 300 RPM spindle speed.  These could be used
> with DD media and formatted to 720K in OS-9.  In this case you don't
> have the magnetic coercivity issue that you get with trying to format
> HD media to low density.  What I've read suggests that the only
> difference between the double density and quad density disks is that
> the QD media have been certified (tested) to work at a track density of
> 96tpi.  Maybe I'll experiment with this and see how well it works on a
> CoCo.
> 
> JCE
> 
> 
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Cheers, Gene
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