Re: Platinum 5.25" drive problem

[mjmahon@aol.com (Michael J. Mahon)]

Ed (noone@nowhere.net) wrote:

>Today, most drives are not as powerful as the media is much more
>sensitive.  Like wise the heads are smaller and constructed
>differently.  I admit it is very unlikely that you will magnatize the
>head, but if you bulk erase a diskette you are looing for trouble.  The
>field on the bulk disk can erase neighbors and cause other difficulties.

Although there is a remotely greater chance of head magnetization
or media demagnetization, the fact is that _no_ recordable magnetic
media supports field strengths sufficient to do very much, unless kept
in close physical contact for a period of time.  Since floppies are in
plastic covers, and usually in a tyvec sleeve, the required degree of
intimacy is unlikely to be achieved.

If you've ever tried to use a magnet to fiddle with a diskette, you
were probably surprised at how strong a magnetic field it took to
actually do anything.  Rule of thumb:  If it won't stick to a refrigerator,
is isn't lilkely to do anything to a diskette.  Now note that no matter
how you magnetize a diskette, it won't stick to a refrigerator.  ;-)
Floppies are relatively poor magnets.

Of course, the head of an Apple disk drive does come into close physical
contact.  But the head is a read/WRITE head, and is driven hard with both
polarities in order to overcome the coercivity of the media to write to it.
This, by definition, overpowers any remanent magnetization of the head.
(That's why there are no disk head demagnetizers.  ;-)

In short, don't worry about using permanent magnets to disrupt the
magnetic patterns recorded on floppys (but don't magnetize the hub
of a 3.5" diskette--that's not good.  ;-).

Also, don't use HD 5.25" diskettes in _any_ Apple II drive, because
it doesn't work and it annoys the diskette.  (Like trying to teach a
pig to sing.  ;-)

HD 3.5" diskettes are not so different in coercivity from DD 3.5"
diskettes, and some drives can write them reliably some of the time.
But since you don't know whether _now_ is one of those times,
you would have to not care much about your data to use them instead
of DD diskettes.

I only say this last part because it continues to come up.  Isn't this
in the FAQ somewhere?

-michael

 Email:  mjmahon@aol.com
 Home page:  http://members.aol.com/MJMahon/