Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!ames!pacbell.com!pacbell!att!cbnewsc!tjr
From: tjr@cbnewsc.att.com (thomas.j.roberts)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 360K Disks Formatted on 1.2M Drives read on 360K Drives
Message-ID: <1990Jun4.170105.4401@cbnewsc.att.com>
Date: 4 Jun 90 17:01:05 GMT
References: <3426@bingvaxu.cc.binghamton.edu>
Organization: AT&T Bell Laboratories
Lines: 47

consp06@bingsuns.cc.binghamton.edu (Robert Konigsberg):
> Here's a wierd one:
> 
> I formatted a 360K Disk on a 1.2M drive using Norton's Safe Format.
> 
> When I brought it to a machine that only had a 360K drive, it wouldn't
> read it.  That's okay, I understand that this could happen due to
> compatability problems.  
> 
> [further discussion deleted]...

I am puzzled by your problems.

I do this all the time, and have NEVER had a problem or a read-error.
I have transferred data from a 1.2Meg drive to a 360kb drive at least
50 separate times, without a single error. The 360kb drive is 5-7 years
old, the 1.2Meg drive is 1 year old; neither has ever been cleaned or
aligned.  I use the DOS v3.3 FORMAT command (FORMAT B: /4) on the 1.2Meg 
drive.  I have no idea what "Norton's Safe Format" is or does.

The key is to use a BRAND-NEW diskette, format it on the 1.2 meg drive,
and NEVER write on it with the 360kb drive. I MEAN NEVER!!!!

	[if you do write on it with the 360kb drive, it can never again
	 be used to do 1.2Meg -> 360kb transfers; it can be used as a
	 normal 1.2Meg OR as a normal 360kb diskette.]

Just think about what is happening - the 1.2Meg head is narrower than the
360kb head, so the 1.2Meg drive can never erase all of what the 360kb drive
wrote (there is space between the 1.2Meg tracks that is covered by the
360kb head, and which slight misalignments can put under the 1.2Meg head).
As long as the inter-track surface is unmagnetized (un-written), misalignments
merely reduce the signal, but don't introduce a WRONG signal; if a signal
has ever been written to the inter-track surface, misalignments can bring
this erroneous signal into the head, making the real signal prone to
errors. As the write head is a bit wider than the read head, problems only
occur 1.2Meg -> 360kb; all other combinations are OK, even in the face of
misalignments (within the specified tolerances for each drive).

	[In desperation, I have occasionally used diskettes which had
	 been written on by 360kb drives - I wiped them off on both
	 sides with a strong magnet before formatting on the 1.2Meg
	 drive. These diskettes were readable without errors on my 360kb
	 drive, but I do not recommend this method.]

Tom Roberts
att!ihlpl!tjrob