Re: Platinum 5.25" drive problem

[Stephen Shaw <xstephenx@apple2.org.za>]

On 10 Jul 2001 22:18:37 GMT, Michael J. Mahon wrote:

> 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.  ;-).

Isn't the hub a light alloy i.e. non-ferrous in which case it will not
magnetize.

>
> 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/

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