Date   : Sun, 21 Mar 2010 21:42:39 +0000
From   : afra@... (Phill Harvey-Smith)
Subject: Re-using floppies

Alex Taylor wrote:
> On 21 March 2010 06:58, Mike Tomlinson <mike@...> wrote:
> 
>> But don't buy HD ones.  Even if they seem to work, they are the wrong
>> spec and you will lose data.

I keep hearing this from the Tandy CoCo folks, despite the fact that it 
goes against my experience with a Sinclair QL (both the CoCo and QL use 
a double density format. 18x256 for the CoCo and 9x512 for the QL), this 
was with a couple of HD pc floppies.

> I've read somewhere that this a combination of the issues of magnetic
> coercivity and the fact that modern HD floppies come preformatted as
> FAT12, so so reformatting them with a double-density format doesn't
> work properly. The same thing I was reading went on to say that the
> disks are close enough in spec to work if you erase them in a bulk
> eraser first, then use them as DD disks. I have no idea if this works
> though, not having access to a bulk eraser.

That sounds plausable, as I believe that HD media do indeed need a 
stronger signal to write to them, so formatting them as DD (in a DD only 
drive) may not completely erase the underlying HD format.

I wonder what happens if you used them in a PC 1.44M drive connected to 
a Beeb (or something else that only does sd/dd), as the disk would be 
detected by the drive as being 1.44, and so it would use the higher 
write current, but because the incoming datarate was only sd/dd that's 
what would get written.

I guess the above might work as long as you ONLY wrote the disk in a 
1.44M drive, I guess reading in a 720K would be fine, but re-writing 
would suffer from the same problem as with the previously PC formatted disk.

I currently have an ok supply of 720K disks so it's not currently a 
problem for me tho....

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.