Substituting DSHD for DSDD disks (or DS2D if you prefer)

Fred Cisin cisin at
Sat Oct 24 21:14:36 CDT 2015

On Sat, 24 Oct 2015, Eric Christopherson wrote:
> I know Chuck Guzis has written about this, but I don't see that he's done
> so publicly in the last few years, so I thought I'd ask here about his and
> others' views on the perennial question of whether (some) 3.5" DSHD disks
> can be reliably used in DSDD-only drives. The oft-repeated claim is that
> writing can appear to work just fine, but that even a few months later read
> errors will occur.

That was certainly the case with 5.25", but THAT was a difference between 
300 Oersted and 600 Oersted.  WAY OFF.

But, with 3.5" disks, the difference is between 600 Oersted and 720? 
Oersted.  THAT is close enough.

For BEST results, I think that it would be better to use the right ones, 
but unlike 5.25" disks, with 3.5", you can get away with it.

> Elsewhere on the page (I don't recall now if it was Herb or Chuck that said
> it) it was conjectured that HD disks that have never been formatted as HD,
> -OR- disks that have gone through a good degaussing, will have better luck
> retaining data. What does everyone think about this? And would an
> electromagnetic library security system (the kind that's like a tube
> through which checked-out materials are put; often with a caution not to
> put tapes or floppies through it) be a suitable degausser?

Probably a very good idea.

Some Windoze machines will check for existing format before formatting, 
and be somewhat uncooperative about reformatting as a different density.

The one time that it is critically important to bulk-erase or use virgin 
disks is when writing 48tpi disks in a 96tpi drive.  When a 96tpi drive 
RE-writes a 48tpi disk, as 48tpi, it can not clear the edges of the track 

Are we really running short of "720K" floppies?
I thought that AOHell had sent out enough snail spam with disks to supply 
us forever!

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