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From: tla@kaiser.UUCP (T Anderson)
Newsgroups: net.micro.pc
Subject: Re: Writing 360K diskettes on 1.2 Mb drives
Message-ID: <411@kaiser.UUCP>
Date: Tue, 28-Oct-86 10:20:59 EST
Article-I.D.: kaiser.411
Posted: Tue Oct 28 10:20:59 1986
Date-Received: Tue, 28-Oct-86 21:41:38 EST
References: <1986Oct26.184138.24015@utcsstat.uucp>
Organization: AT&T Bell Laboratories, Liberty Corner
Lines: 35

I've had good luck writing 360K disks on several varieties of 96TPI
drives including 1.2 Mb drives on an AT, 800K drives on an Eagle 1620
and others.  The normal difficulty seems to be that the write heads
on the 96TPI drives is only half as wide and so when used in the
360K mode only reads and writes half the track used by the normal
360K drives.  This means that reading is never a problem, but when
you write it only changes the information on half of the track.  If
read back on a 96TPI drive there is no problem (since it only reads
the half anyway), but when read on a normal 360K drive the wider
head sees conflicting data on the two halves of the track and
concludes that the disk is not formatted.  
  
There seems to be no way to write both halves of the track with the
narrow heads and keep them aligned accurately enough to read back
correctly on 360K disk UNLESS the other half is BLANK.  The solution
I've used without a failure is to use virgin disks (ones never
formatted).  Format them on the 1.2M drive requesting the 360k
density.  This means that the other half of each track is not even
formatted (random magnetic patterns).  Then write whatever is
desired on the disk.  It may now be read on a 360K drive. BUT NEVER
WRITE TO IT USING A 360 K DRIVE.  If you ever write to it the other
half track will get used and the 1.2M drive will never be able to
change that half.  The totally unformatted half has such a weak
magnetic signal that it causes no problem.

Thus you need different disks to copy back and forth, esp in the
1.2M to 360K direction.  You have to keep a special disk never
written to by a 360K drive just to use for transferring.  This is a
small nuisance but seems to work everytime.  I have considered
trying to use disks that have been demagnetized by a bulk tape
demagnetizer to see if they work but have never done it.

			-- Terry L Anderson
			   AT&T Bell Laboratories - Liberty Corners
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