On Sat, Oct 24, 2015 at 9:14 PM, Fred Cisin <cisin at xenosoft.com> wrote:
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
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.
OK. I just wanted to ask, in case running a floppy through that contraption
would actually mess up its magnetization so badly that it couldn't then be
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
I had to laugh at that. Another list member recently told me that AOL disks
are the ones he's had the most success with recently. I don't know how many
of them were 720KB, though. In any case, I think I only started getting AOL
dis(c|k)s in the CD-ROM era, unfortunately.
But anyway, it does look like DD disks are more expensive; that, coupled
with the fact that a lot of HD disks in the wild are going to be newer,
makes me want to buy some HD ones instead. But that second part might be
more of a bad thing, if it's true that floppy QA went downhill later on.
On Sat, Oct 24, 2015 at 10:48 PM, Chuck Guzis <cclist at sydex.com> wrote:
My opinions on Herb's retrotechnology site still
hold--with one addition.
Thanks for that.
You can sometimes get 3.5" HD disks that have been used, but now refuse to
accept a format by first performing a DC erase. That is, get a very strong
rare-earth magnet, and moving in a helical path (i.e. circular, starting
close to the disc, slowing moving away), perform an erase pass. Following
with an AC erase can sometime inject new life into the disk. I've tried
this several times and it does seem to work.
Fascinating -- I didn't know there were AC and DC magnetic fields. How
strong is "very strong", and would the library device I mentioned count
toward "an AC erase"? Should I assume that just doing an AC erase would be