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From: ugfailau@sunybcs.uucp (Fai Lau)
Newsgroups: comp.sys.ibm.pc
Subject: Re: new floppy format proposal
Message-ID: <6373@sunybcs.UUCP>
Date: Sat, 7-Nov-87 22:52:55 EST
Article-I.D.: sunybcs.6373
Posted: Sat Nov  7 22:52:55 1987
Date-Received: Tue, 10-Nov-87 04:57:49 EST
References: <4289@cit-vax.Caltech.Edu> <1155@cup.portal.com>
Sender: nobody@sunybcs.UUCP
Reply-To: ugfailau@joey.UUCP (Fai Lau)
Organization: SUNY/Buffalo Computer Science
Lines: 51
Keywords: high-density floppy

In article <300@gethen.UUCP> farren@gethen.UUCP (Michael J. Farren) writes:
...
>>roatation speed, if there is any. And off cause, you can
>>always write a high density disk with a normal drive..
>
>No you can't.  Not reliably.  Regardless of whether or not the coating
>on a HD diskette is physically similar to the coating on a normal
>drive, the media has a higher coercivity, thus requiring a different
>head assembly, one which can produce the levels of flux required to
>change the state of the media.  Normal drives don't have it.
>
	Thanx for the comment. You're quite right. However, it only
applies in the situation where the coercivity of the media is indeed
higher than that of its regular density counterpart.
	In order to make a magnetic media HD suitable, there are
two things that should be done. One is to reduce the size of the
magnetic particles. Second is to increase its coercivity.
When the size of the magnetic particles are reduced, a narrower
track of a higher frequency signal can be recorded on the media,
while the maximum output level of the media increases. However, since
the increase of this output level due to the smaller particle size and
more densly packed particles generally does not adequately compensate
the decrease in the output level resulted from the
increase of signal frequency and narrowing of the recording
track (the higher frequency the signal you write on
a magnetic media, the lower it's output would be.
Except where the frequency is *very* low), soemthing
is usually done to the coercivity of the magnetic material to increase
its output level (and of course, to make it more stable).
	For a 5.25 HD disk instead of the mini 3.5 disk, I
don't know if the increase of the coercivity is warranted
to generate enough output signal strength. I am not
sure. If no increase is made, then the disk is indeed
usable in a regular density drive. But for something like
3.5 minidisk, such increase is a must.
	BTW, most of the time when the density of the magnetic
particles is increased on a media, their "shape" is changed, too.
They're more needle like and more uniform.

>My intuition is that the coatings of a normal diskette and a HD diskette
>are, in fact, quite different.  I don't have proof of this, but they
>look different to my eye.
>
	When a different type or chemistry of the magnetic particles is
used on a HD disk, it'll look different. But a mere change in
the size and shape of the particles should yield no visual difference.

Fai  Lau
SUNY at Buffalo (The Arctic Wonderland)
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