Using a 1.44MB 3.5inch floppy on an old controller

From: jpero_at_sympatico.ca <(jpero_at_sympatico.ca)>
Date: Sun Apr 22 09:06:11 2001

> Date: Sun, 22 Apr 2001 11:42:15 -0500
> From: Michael Brutman <mbbrutman_at_chartermi.net>
> To: classiccmp_at_classiccmp.org
> Subject: Using a 1.44MB 3.5inch floppy on an old controller
> Reply-to: classiccmp_at_classiccmp.org

> I have a few PCjrs running around, and I've often thought of
> either adding 3.5" drives to them, or replacing the standard
> 5.25" drive with 3.5" drives. The controller only supports
> double density data rates (250?), so I'm limited to 720KB
> 3.5" drives. These are getting hard to find.

Correct, only source of this 720K drives are from scrapped machines.
That 720K drives must be very few in number compared to 360K and
1.22M drives.

> a 360kb image prepared on a Linux machine), and it also ran
> diagnostics. So now I'm confused - why did it work?

You have answer. :-) I did this too before on XT and odd balls for
that reason. Also Dos 3.3 supports 720K natively.

Both 720K and 1.44MB are same layout only in 80 tracks only
differences are in type of media and number of sectors per track. 9
for 720K and 18 sectors for 1.44MB. Spun at same 300rpm, therefore
same data rate on 720K due to 9 sectors and also same thing for 360K
except it is 40 tracks. For single sided 180K that's same story, 9
sectors.

>
> Does the modern 1.44MB drive sense that the controller is
> only sending data at 250KHz rate? If so, how is it doing
> the sensing? (The reduced write-current pin (2) isn't
> being used - I verified that with a meter.)

That is input not output, controlled by the controller side also the
drive itself automatically change write current also when it sense on
type of floppy itself via that hole. I think.

Cheers,

Wizard
Received on Sun Apr 22 2001 - 09:06:11 BST