Looking at Wikipedia, the 3.5" DD format supports both 40 tracks and 80 tracks.
https://en.wikipedia.org/wiki/List_of_floppy_disk_formats#Physical_composition

And yes there is a difference in the magnetic media for DD and HD too, using a DD head and the write currents for a DD head would not work well with HD media.
https://en.wikipedia.org/wiki/Coercivity





On 8/8/2017 10:53 AM, John Gardner wrote:
So flipping a  3.5"  floppy <would> work,  if the housing for the disk

would let you do that.  Hmm...

And the reason HD disks are unreliable is that the signal returned

by the media when reading the disk is (presumably) too high?

Interesting...

  ...


On 8/8/17, biggran...@tds.net <biggran...@tds.net> wrote:
The specifications in the PDF for the PDD1 and PDD2 says the following:
PDD1 (26-3808):
Disk
      Number of surfaces                        1
      Number of Memory Blocks
          Total number of tracks               40
          Total number of hard sectors    80


PDD2 (26-3814):
Disk
      Number of surfaces                        1
      Number of Memory Blocks
          Total number of tracks               80
          Total number of hard sectors    160






On 8/8/2017 12:39 AM, Gary Weber wrote:
Double-sided doesn't hurt anything of course, although it's too bad you
can't make
3.5" flippy disks as easily as you could 5.25"!

After rereading this I wanted to make one critical point.   Remember,
if yours is truly the TPDD2, it already is double sided.  It formats
the drive as 100K per side (200K total).  You use the "Bank" feature
in TS-DOS to switch between which side you're accessing.   So, no need
to be fantasizing about flippy-floppies.  ;-)

It was the original TPDD that is only 100K single sided.

Gary


On Mon, Aug 7, 2017 at 8:04 PM, Kurt McCullum <kurt.mccul...@att.net
<mailto:kurt.mccul...@att.net>> wrote:

     Thanks Brian & Garry,

     I suspected that to be the case but when my HD disk appeared to
     work I thought I would ask.

     Kurt

     *From:*M100 [mailto:m100-boun...@lists.bitchin100.com
     <mailto:m100-boun...@lists.bitchin100.com>] *On Behalf Of *Brian
White
     *Sent:* Monday, August 07, 2017 4:41 PM
     *To:* m...@bitchin100.com <mailto:m...@bitchin100.com>
     *Subject:* Re: [M100] 3.5" Media

     I wasn't using these when they were current, but... No question
     double density. Aside from the dates when these things were sold,
     or the fact that the actual formatting is far less than double
     density, or the fact that the original utility disk that came with
     it is double density, which are each solid points on their own...

     The manual for PDD-2 says to use cat 26-415 or 26-416,

     and those catalog numbers are not only double density but actually
     single sided.

     Double-sided doesn't hurt anything of course, although it's too
     bad you can't make 3.5" flippy disks as easily as you could 5.25"!

     But trying to use SD/DD read/write head signal strength on HD
     media is going to either not work at all, or work very
     poorly/unreliably, or worse, *appear to work but be corrupt*.
     Because the HD media is more sensitive than the older media, and
     operates at lower signal strengths than the older media. An SD or
     DD drive write signal is stronger to match the weaker media it was
     meant for. So in effect you are over-driving the newer media. In
     plain audio you can tell when that's happening because you
     actually hear the distortion like a ripped speaker. As data, you
     can't hear it directly or tell it's happening, which makes it more
     dangerous. They should have made HD disks so they don't even fit
     in older drives. Make them slightly longer maybe, so that old
     disks could still fit in new drive, but new disks couldn't fit in
     old drives. The guy who sent me my copy of the utility disk sent
     one of each type, and the HD copy actually works, which is what I
     mean by "dangerous", because, going by that, you would conclude
     "It works, so, it works."

     Jump to page 6

http://www.classiccmp.org/cini/pdf/Tandy/Portable%20Disk%20Drive%202%20Operation%20Manual.pdf

<http://www.classiccmp.org/cini/pdf/Tandy/Portable%20Disk%20Drive%202%20Operation%20Manual.pdf>

     Jump to page 41

http://www.colorcomputerarchive.com/coco/Documents/Radio%20Shack%20Catalogs/Tandy%20Computer%20Catalog%20and%20Software%20Reference%20Guide%20(1988)(Tandy).pdf

<http://www.colorcomputerarchive.com/coco/Documents/Radio%20Shack%20Catalogs/Tandy%20Computer%20Catalog%20and%20Software%20Reference%20Guide%20%281988%29%28Tandy%29.pdf>

     That catalog doesn't say DD explicitly, but it does say others are
     HD and 1.44M explicitly, which makes everything else not-HD by
     omission.

     I assume that somewhere a more authoritative reference on the
     catalog numbers would show that more explicitly.

     --

     bkw

     On Mon, Aug 7, 2017 at 6:41 PM, Gary Weber <g...@web8201.com
     <mailto:g...@web8201.com>> wrote:

         Double Density for sure.  A long time ago, I had attempted to
         format a
         high density disk on a TPDD2 but it gave an error.   I've
         always had
         to use double density disks.


         On Mon, Aug 7, 2017 at 2:33 PM, Kurt McCullum
         <kurt.mccul...@att.net <mailto:kurt.mccul...@att.net>> wrote:
         > For those who have used a TPDD2 in the past, I have a
         question about media
         > type. Do these drives prefer double density (720k) or high
         density (1.44mb)
         > media? I've tested with both from by using recycled media
         from years gone by
         > and both seem to work. My primary interest in the drive is
         to see if I can
         > improve mComm but as I'm testing, I'd like to actually use
         the proper media.
         >
         > Kurt
         >


         --
         Gary Weber
         g...@web8201.com <mailto:g...@web8201.com>




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