Using a 1.44MB 3.5inch floppy on an old controller - test-drb@ccmp.vtda.org

22 Apr 2001

From: Michael Brutman &lt;mbbrutman(a)chartermi.net&gt;
...
 I know that the drive senses the media and adjusts the
write
current accordingly, to get around a bug in older drive
controllers.  But I'm still confused about how the drive
talks to the controller.  The PCjr will still try to format
a HD disk - it will just fail. 

3.5" drives have no intelligence.  There are signals that 
result from switches that the controller monitors and interprets.
The media in place and media type switches are two such cases.
They can be optical or mechanical but that's not a factor.

...
 I'm not a hardware engineer, but it would seem
reasonable to
me that the controller and the drive always talk at the 250KHz
rate, because the controller can't do anything else.  For
double density media this is fine, and the 1.44MB drive looks
and smells just like a real 720KB drive.  However, upon using
a high density disk, commands to read and write data fail
because the drive knows it has high density media, but it is
still talking to the floppy controller at 250KHz (instead of
500KHz). 

The controller or the drive does do some limited things based 
on media sensor switch and that is why you must block the 
hole to make it work.

Allison

...

Is this correct?  Or does the drive sense that it has
high density media, adjust it's data transfer rate to 500KHz,
and then fail because the controller doesn't know what's
going on?

While we're on the topic, what do people use for archiving
copy protected disks?  I've tried older versions of TeleDisk,
but it really has a hard time with Sargon III which makes me
wonder if it is working reliably on my other titles.

Thanks,
Mike 