Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!uw-beaver!tektronix!tekcrl!tekfdi!videovax!stever
From: stever@videovax.tv.Tek.com (Steven E. Rice, P.E.)
Newsgroups: comp.sys.amiga
Subject: DD vs. HD floppies (was Re: Professional Page 1.2 is out)
Summary: yes
Keywords: DD, HD, floppies, coercivity
Message-ID: <5452@videovax.tv.Tek.com>
Date: 21 Jun 89 19:12:16 GMT
References: <20116@sunb.UUCP> <735@lakesys.UUCP> <6597@cs.Buffalo.EDU> <741@lakesys.UUCP>
Reply-To: stever@videovax.tv.tek.com.UUCP (Steven E. Rice, P.E.)
Organization: Tektronix TV Measurement Systems, Beaverton OR
Lines: 25

In article <741@lakesys.UUCP>, Joe Pantuso (joe@lakesys.UUCP) writes:

> I recieved some ds/hd (pc type) disks courtesy of Adobe a few months back
> and I attempted to format and use them, out of six disks only ONE of them  
> worked.  Is there really that much of a physical difference between dd and hd
> disks?  . . .

The "HD" floppies hold twice as much data as "DD" floppies by doubling the
data clock rate.  This makes the magnetic domains on the HD disks one-half
the size of the domains on the DD disks.  To ensure they won't self-erase
(two "1" bits surrounding a "0" bit causing the "0" to become a "1", or
vice versa), the magnetic material used in HD disks has higher coercivity
(just what it sounds like -- you have to work harder to coerce [force] the
magnetism to change direction).

HD disk material requires higher write currents because of the higher
coercivity of the oxide.  Your chances of correctly writing an HD disk
in a drive designed only for DD disks are pretty small. . .

					Steve Rice

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